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TCL 4 Series/S425 2019
TV REVIEW

Usage Ratings - Version 1.3
7.3
Mixed Usage
Value for price beaten by
: none
6.4
Movies
7.0
TV Shows
7.1
Sports
8.4
Video Games
6.6
HDR Movies
7.9
HDR Gaming
8.1
PC Monitor
Type : LED
Sub-Type
:
VA
Resolution : 4k

The TCL 4-Series S425 Roku Smart TV is a decent TV with decent picture quality. It can display deep blacks thanks to its high native contrast ratio, but lacks a local dimming feature to improve dark room performance. It has good reflection handling, but limited brightness both in SDR and in HDR, and doesn't perform well in a bright room. It does not have a wide color gamut and can't deliver HDR content with vivid colors and bright highlights. It has a very fast response time, and fast-moving content has only minimal blur trail. The input lag is very low, and this will please gamers and PC users.

Test Results
Design 6.5
Picture Quality 7.1
Motion 6.8
Inputs 9.6
Sound Quality 6.3
Smart Features 7.5
Pros
  • Very low input lag, great for games.
  • Great smart features.
Cons
  • Can't get bright enough.
  • Image degrades when viewed at an angle.

Check Price

Market Context

The TCL 4-Series S425 is a budget VA panel TV. It sits below the TCL S517. It is the replacement of last year's TCL S Series S405. The TCL S425 is comparable to most budget models of other manufacturers like the Samsung RU7100, the LG UK6300, or Vizio E Series 2018.

6.5

Design

Curved : No

The TCL S425 has a decent design. It has a wide plastic stand that supports it well, but the TV will wobble if nudged. The back of the TV is very similar to last year's TCL S405. The top half is metallic, whereas the bottom part and the body are plastic. It is not very thick and will not protrude much if wall-mounted. The build quality is decent, and you should not have any issues with it.

Stand

The stand of the TCL S425 is plastic and supports the TV well. It is black and almost as wide as the TV. Last year's TCL S405 had a very similar stand, but with a silver finish. The legs cannot be reversed, and the TV will wobble if nudged.

Footprint of the 55" model stand: 32.2" x 7.3"

Back
Wall Mount : VESA 100x100

The back of the TV is plain. The top part is metal, whereas the bottom half and the rest of the body are plastic. The TCL S425 is available in many sizes and not all of them fit the same VESA mount size. Check here to see which VESA mount size is suitable for each TV size.

There is no cable management.

Borders
Borders : 0.59" (1.5 cm)

The borders are plastic, very plain, and have an average thickness.

Thickness
Max Thickness : 2.91" (7.4 cm)

The TV has an average thickness when viewed from the side, and it will not stick out much if wall-mounted.

Temperature
Maximum Temperature
:
96 °F (35 °C)
Average Temperature
:
85 °F (29 °C)
6.5 Build Quality

The build quality is decent. There are no gaps or loose ends, and although the TV does not have a premium look, you should have no issues with it.

7.1

Picture Quality

The TCL 4-Series has a decent picture quality. It has a high native contrast ratio that delivers deep blacks in a dark room but unfortunately, it lacks a local dimming feature to further improve dark room performance. The S425 cannot get very bright and it is more suitable for a dim room. It can handle reflections well but has narrow viewing angles and it is not suitable for a room with a wide seating arrangement. It doesn't have a wide color gamut and can't deliver HDR content with vivid colors and highlights that pop. Finally, the gray uniformity is decent, but some sports fans might find the amount of dirty screen effect bothersome.

9.1 Contrast
Native Contrast
:
6054 : 1
Contrast with local dimming
:
N/A

The native contrast ratio of the TCL S425 is excellent. Blacks look deep in a dark room and this great for the picture quality. It is a significant improvement over last year's TCL S405. Unfortunately, the TV lacks a local dimming feature and can't improve the appearance of blacks further.

0 Local Dimming
Local Dimming
:
No
Backlight
:
Direct

The TCL S425 does not have a local dimming feature. The video is for reference only.

5.4 SDR Peak Brightness
SDR Real Scene Peak Brightness
:
168 cd/m²
SDR Peak 2% Window
:
142 cd/m²
SDR Peak 10% Window
:
177 cd/m²
SDR Peak 25% Window
:
177 cd/m²
SDR Peak 50% Window
:
177 cd/m²
SDR Peak 100% Window
:
177 cd/m²
SDR Sustained 2% Window
:
141 cd/m²
SDR Sustained 10% Window
:
177 cd/m²
SDR Sustained 25% Window
:
177 cd/m²
SDR Sustained 50% Window
:
177 cd/m²
SDR Sustained 100% Window
:
177 cd/m²
SDR ABL
:
0.017

Disappointing SDR peak brightness for the S425. The performance is in the same ballpark figure as last year's TCL S405. This TV is okay for a moderately lit room, but it is not suitable for a bright room. Except for small highlights, the brightness remains unchanged no matter the scene, and this is good.

We performed our measurements after calibration with picture mode set to ‘Movie.’ Different settings may produce a brighter picture.

You can check our settings page to see how to set the brightness.

5.1 HDR Peak Brightness
HDR Real Scene Peak Brightness
:
191 cd/m²
HDR Peak 2% Window
:
199 cd/m²
HDR Peak 10% Window
:
206 cd/m²
HDR Peak 25% Window
:
207 cd/m²
HDR Peak 50% Window
:
207 cd/m²
HDR Peak 100% Window
:
207 cd/m²
HDR Sustained 2% Window
:
199 cd/m²
HDR Sustained 10% Window
:
206 cd/m²
HDR Sustained 25% Window
:
207 cd/m²
HDR Sustained 50% Window
:
207 cd/m²
HDR Sustained 100% Window
:
207 cd/m²
HDR ABL
:
0.003

The TCL S425 has poor HDR peak brightness and can't display bright HDR highlights. Just like in SDR, the brightness remains unchanged no matter the scene. This is a similarly bad performance to last year's TCL S405.

We performed our measurements without calibration with picture mode set to ‘dark HDR' and 'brighter.' Different settings may produce a brighter picture.

You can check our settings page to see how to set the HDR settings.

6.8 Gray Uniformity
50% Std. Dev.
:
2.926 %
50% DSE
:
0.203 %
5% Std. Dev.
:
3.116 %
5% DSE
:
0.112 %

The TCL 4-Series has decent gray uniformity. The corners are a little darker, and some dirty screen effect can be seen at the center of the screen, which might disappoint sports fans. Unfortunately, in near-dark scenes, there are noticeable uniformity issues on both sides of the screen, but the uniformity is better in the center.

4.8 Viewing Angle
Color Washout
:
19 °
Color Shift
:
23 °
Brightness Loss
:
27 °
Black Level Raise
:
15 °
Gamma Shift
:
12 °

The S425 has bad viewing angles. This is typical for VA panel TVs. As soon as you move off center, the image loses accuracy as gamma shifts, black levels rise, and colors start to wash out. This is similar behavior to last year's TCL S Series S405. This TV is not a good choice if you have a room with a wide seating arrangement. If viewing angles are important to you, then check out the LG UK6300.

7.3 Black Uniformity
Native Std. Dev.
:
1.142 %
Std. Dev. w/ L.D.
:
N/A

The black uniformity on the TCL S425 is decent. There is visible backlight bleed at the edges which, however, is only noticeable when you watch a very dark scene in a dark room.

7.8 Reflections
Screen Finish
:
Semi-gloss
Total Reflections
:
5.3 %
Indirect Reflections
:
0.6 %

The handling of reflections on the TCL 4-Series is good. The TV has a semi-glossy finish that limits indirect reflections. You should have no problem placing this TV in a room with many small light sources. However, if you place it across from a large window, reflections might become bothersome.

5.9 Pre Calibration
White Balance dE
:
3.36
Color dE
:
5.69
Gamma
:
2.33
Color Temperature
:
6130 K
Picture Mode
:
Movie
Color Temp Setting
:
Warm
Gamma Setting
:
2.2

Unfortunately, the out-of-the-box color accuracy for the TCL S425 is disappointing. The errors we measured both in the white balance dE and in the color dE are large. The color error especially might be noticeable by many. The TV is clipping reds and whites when not in PC mode. In order to see a significant improvement, you would have to lower the contrast a lot, but we do not recommend it as it affects the picture quality. The color temperature is warmer than the 6500K target, and thus the image has a slight reddish and yellow tint. The gamma does not follow the target, and thus dark scenes are significantly darker than they should be.

9.1 Post Calibration
White Balance dE
:
0.50
Color dE
:
2.10
Gamma
:
2.22
Color Temperature
:
6532 K
White Balance Calibration
:
11 point
Color Calibration
:
Yes
Auto-Calibration Function
:
No

After calibration, the accuracy of the TCL S425 is excellent. It is almost impossible to spot any remaining white balance inaccuracies. On the other hand, some color inaccuracies, mainly in the reds and the greens, remain after calibration and some enthusiasts might be able to spot them. Just like with other TCL TVs, calibration is only possible via the mobile app, but you still need to use a colorimeter.

You can see our recommended settings here.

8.0 480p Input

Upscaling of low-quality content such as DVDs is good.

8.0 720p Input

720p sources such as cable are upscaled well. Details remain clear.

9.0 1080p Input

Upscaling of 1080p content such as Blu-rays or game consoles looks good with no obvious issues.

10 4k Input

Native 4k content has no issues.

7.2 Color Gamut
Wide Color Gamut
:
No
DCI P3 xy
:
80.17 %
DCI P3 uv
:
86.24 %
Rec 2020 xy
:
57.74 %
Rec 2020 uv
:
63.53 %

The TCL S425 does not have a wide color gamut. The true color gamut of the TV is shown by the maximum red, green, and blue in the Rec 2020 gamut picture. Unfortunately, all other colors in the Rec 2020 picture and all the P3 colors are undersaturated. We assume that this happens because the TV is prioritizing brightness over color accuracy because it is so dim. These tests were done at 75% brightness stimulus. When we performed the same tests at a dimmer 50% stimulus the accuracy was much better as can be seen in the following images:

The TV's EOTF is dimmer than the PQ curve, and at about 50% stimulus gray it starts to roll off very early to smooth the transition to the TV's low peak brightness. The same performance is found in 'Game' mode as you can see here.

If you wish to make the HDR brighter, you can set gamma to 1.8 in the phone app. This will result in this EOTF which is a little brighter than before.

6.3 Color Volume
Normalized DCI P3 Coverage ITP
:
70.9 %
10,000 cd/m² DCI P3 Coverage ITP
:
22.8 %
Normalized Rec 2020 Coverage ITP
:
55.7 %
10,000 cd/m² Rec 2020 Coverage ITP
:
17.8 %

The TCL 4-Series has mediocre color volume. The TV can't display very dark saturated colors. When the TV is trying to display bright P3 colors, the gamut narrows significantly, probably due to the TV's tone mapping prioritizing brightness over color accuracy because the TV is so dim.

8.3 Gradient
Color Depth
:
10 Bit
Red (Std. Dev.)
:
0.099 dE
Green (Std. Dev.)
:
0.109 dE
Blue (Std. Dev.)
:
0.084 dE
Gray (Std. Dev.)
:
0.109 dE

The gradient of the TCL S425 is very good. Very little banding is visible, especially in darker shades of green and gray, but nothing major. Overall, it performs slightly worse than last year's S405 and a little better than the Samsung NU7100.

10 Temporary Image Retention
IR after 0 min recovery
:
0.00 %
IR after 2 min recovery
:
0.00 %
IR after 4 min recovery
:
0.00 %
IR after 6 min recovery
:
0.00 %
IR after 8 min recovery
:
0.00 %
IR after 10 min recovery
:
0.00 %

There is no temporary image retention on the TCL S425.

10 Permanent Burn-In Risk
Permanent Burn-In Risk
:
No

We don't expect VA panels to experience permanent image retention, as the VA panel in our long-term test appears immune.

Pixels
6.8

Motion

The motion handling of the TCL S425 is decent. It has a very fast response time, so there is only a little blur behind fast-moving content. Below a certain brightness level, it uses PWM to dim the backlight, which might bother some people. There are no extra features to enhance motion handling, and unfortunately, the TV can only remove judder from true 24p sources.

8.9 Response Time
80% Response Time
:
4.7 ms
100% Response Time
:
12.1 ms

The response time of the S425 is excellent. Only a short trail follows fast-moving objects. In dark scenes, however, some smearing may be present due to the longer transition between darker shades, such as from 0% to 20%. Nonetheless, this is an improvement over last year's S405.

4.0 Flicker-Free
Flicker-Free
:
No
PWM Dimming Frequency
:
120 Hz

The TV uses PWM to dim the backlight, but only below 17/100 backlight setting. Backlight PWM dimming results in a 120Hz flicker which might bother some people. This is very different behavior than the TCL S405, which used PWM dimming throughout the entire range of its backlight levels.

5.4 Black Frame Insertion (BFI)
Optional BFI
:
No
Min Flicker for 60 fps
:
120 Hz
60 Hz for 60 fps
:
No
120 Hz for 120 fps
:
N/A
Min Flicker for 60 fps in Game Mode
:
120 Hz

Just like last year's S405, the S425 can't reduce its flicker frequency to 60Hz to make the image look crisper. However, at lower brightness levels, its 120Hz PWM backlight does help somewhat to make motion look clearer.

0 Motion Interpolation
Motion Interpolation (30 fps)
:
No
Motion Interpolation (60 fps)
:
No

The S425, just like last year's S405, doesn't provide any motion interpolation feature.

7.2 Stutter
Frame Hold Time @ 24 fps
:
29.6 ms
Frame Hold Time @ 60 fps
:
4.6 ms

The TCL 4-Series has a little stutter due to the very fast response time that results in a higher frame hold time of 24p content, like movies. Unfortunately, the TV does not offer any option to help you reduce stutter.

5.6 24p Judder
Judder-Free 24p
:
Yes
Judder-Free 24p via 60p
:
No
Judder-Free 24p via 60i
:
No
Judder-Free 24p via Native Apps
:
No

Unfortunately, the TCL S425 can only remove judder from 24p movies when they are played from 24p sources like DVDs or Blu-rays. 24p movies played from 60p/60i sources like cable, satellite boxes, or even through the native apps will have some judder.

There is no specific feature or option to turn on so as to remove judder from 24p movies on 24p sources. The TV detects it and displays the movie properly.

0 Variable Refresh Rate
Native Refresh Rate
:
60 Hz
Variable Refresh Rate
:
No
4k VRR Maximum
:
N/A
4k VRR Minimum
:
N/A
1080p VRR Maximum
:
N/A
1080p VRR Minimum
:
N/A
1440p VRR Maximum
:
N/A
1440p VRR Minimum
:
N/A
VRR Supported Connectors
:
N/A

The S425 has a 60Hz panel and does not support more advanced features such as FreeSync.

9.6

Inputs

The S425 has a very low input lag that will please gamers. It supports the most common resolutions and can display proper chroma 4:4:4 as long as you set the input icon to 'Computer.' When you connect a PC to the TV, it automatically switches and locks to PC mode.

9.8 Input Lag
1080p @ 60 Hz
:
12.9 ms
1080p @ 60 Hz Outside Game Mode
:
48.6 ms
1440p @ 60 Hz
:
12.8 ms
4k @ 60 Hz
:
13.0 ms
4k @ 60 Hz + 10 bit HDR
:
12.9 ms
4k @ 60 Hz @ 4:4:4
:
13.0 ms
4k @ 60 Hz Outside Game Mode
:
29.7 ms
4k @ 60 Hz With Interpolation
:
N/A
8k @ 60 Hz
:
N/A
1080p @ 120 Hz
:
N/A
1440p @ 120 Hz
:
N/A
4k @ 120 Hz
:
N/A
1080p with Variable Refresh Rate
:
N/A
1440p with VRR
:
N/A
4k with VRR
:
N/A
8k with VRR
:
N/A
Auto Low Latency Mode (ALLM)
:
Yes

The TCL S425 has excellent low input lag. To get the lowest input lag, you need to switch the Game Mode to 'On.' The Game Mode is available in all picture modes. During our test, there we times where we had to turn off the TV or disconnect and reconnect the HDMI to get the lowest input lag. We assume that this was due to an issue with the HDMI handshake. When we changed to 'Game Mode' it went to an in-between state that had a higher input lag. This should not be a common issue to most users.

When you connect a PC, it is always detected automatically, and you do not have to do anything special to display proper chroma subsampling 4:4:4. To display 4:4:4 through other sources, change the icon to Computer.

8.3 Supported Resolutions
1080p @ 60 Hz @ 4:4:4
:
Yes
1080p @ 120 Hz
:
No
1440p @ 60 Hz
:
Yes (native support)
1440p @ 120 Hz
:
No
4k @ 60 Hz
:
Yes
4k @ 60 Hz @ 4:4:4
:
Yes
4k @ 120 Hz
:
No
8k @ 30 Hz or 24 Hz
:
No
8k @ 60 Hz
:
No

The TCL S425 supports most common resolutions at 60Hz, but it can't display any resolution at 120Hz. Chroma 4:4:4 works properly with a PC even if the icon on the input is not set to 'computer.' For other sources, change the icon to 'computer.'

To set an HDMI port to full bandwidth 2.0, follow this sequence: Settings > TV Inputs > HMDI1 (for port 1) > HDMI Mode > HDMI 2.0.

When you connect a PC, the TV switches automatically to PC mode. There is no way to use the TV with a PC and be outside of PC mode.

Input Photos
Total Inputs
HDMI : 3
USB : 1
Digital Optical Audio Out : 1
Analog Audio Out 3.5mm : 1
Analog Audio Out RCA : 0
Component In : 0
Composite In : 1 (incl. adapter)
Tuner (Cable/Ant) : 1
Ethernet : 1
DisplayPort : 0
IR In : 0
SD/SDHC : 0
Inputs Specifications
HDR10
:
Yes
HDR10+
:
No
Dolby Vision
:
No
HLG
:
No
3D
:
No
HDMI 2.0 Full Bandwidth
:
Yes (HDMI 1,2,3)
HDMI 2.1
:
No
CEC : Yes
HDCP 2.2 : Yes (HDMI 1,2,3)
USB 3.0
:
No
Variable Analog Audio Out : Yes
Wi-Fi Support : Yes (2.4 GHz, 5 GHz)

The S425 supports CEC, but we were unable to make it work with our Blu-ray player.

Audio Passthrough
ARC
:
Yes (HDMI 3)
eARC support
:
No
Dolby Atmos via TrueHD via eARC
:
No
DTS:X via DTS-HD MA via eARC
:
No
5.1 Dolby Digital via ARC
:
Yes
5.1 DTS via ARC
:
Yes
5.1 Dolby Digital via Optical
:
Yes
5.1 DTS via Optical
:
Yes

If you wish to enable Dolby over ARC, you must select the Dolby D/DTS setting.

6.3

Sound Quality

The TCL has a mediocre sound. It can't get very loud but is able to produce clear and intelligible dialogue. Unfortunately, its bass is lacking and doesn't have any body or thump to it. The TCL S425 has no room correction system but its distortion performance is decent. For a better sound, dedicated speakers or soundbars are recommended.

6.2 Frequency Response
Low-Frequency Extension
:
134.54 Hz
Std. Dev. @ 70
:
3.19 dB
Std. Dev. @ 80
:
3.20 dB
Std. Dev. @ Max
:
5.27 dB
Max
:
86.2 dB SPL
Dynamic Range Compression
:
3.80 dB

The S425 has a mediocre frequency response. LFE (low-frequency extension) is at 135Hz, which is poor. This means that this TV won't have any thump or punch to its bass. The response above the LFE point is good, so dialogue will be clear and intelligible. It can get reasonably loud, but not loud enough for noisy environments.

6.6 Distortion
Weighted THD @ 80
:
0.215
Weighted THD @ Max
:
0.764
IMD @ 80
:
3.73 %
IMD @ Max
:
14.73 %

The distortion performance of the TCL S425 is decent. Although it won't be noticeable in most cases, the TCL S324 has a relatively elevated amount of distortion. However, the jump in THD at max volume is not very large, which is good.

7.5

Smart Features

Smart OS : Roku TV
Version : 9.0

The TCL 4-Series runs the Roku TV Smart OS. It is very easy to use and runs smoothly without issues. Unfortunately, there are ads from which you can not opt out.  It has a very large number of apps, that Roku calls 'Streaming Channels,' where you'll find what you need. The remote is very basic, but the remote app offers some neat features like voice control.

8.0 Interface
Ease of Use
:
Easy
Smoothness
:
Very Smooth
Time Taken to Select YouTube
:
4 s
Time Taken to Change Backlight
:
4 s
Advanced Options
:
Many

The Roku interface is very responsive, with smooth animations and almost no lag. The navigation menu is easy to use. However, nearly all navigation must pass through the home menu, which can be tiring at times.

0 Ad-Free
Ads
:
Yes
Opt-out
:
No
Suggested Content in Home
:
Yes
Opt-out of Suggested Content
:
No

We saw no ads during our testing, but the TCL TVs are known to have ads as you can see on the S405. You can opt out of personalized ads, but you will still get ads that are not targeted. To opt out of personalized ads, you must enable the 'Limit ad tracking' option in the Advertising menu.

8.0 Apps and Features
App Selection
:
Many
App Smoothness
:
Average
Cast Capable
:
Yes
USB Drive Playback
:
Yes
USB Drive HDR Playback
:
Yes
HDR in Netflix
:
Yes
HDR in YouTube
:
Yes

The TCL S425 has a very large number of apps. The Roku interface calls its apps 'Streaming Channels,' but they work like normal apps. It is a very versatile interface that allows you to do many things like casting from your phone or playback from a USB, among other things.

6.0 Remote
Size
:
Small
Voice Control
:
No
CEC Menu Control
:
No
Other Smart Features
:
No

The remote is very basic. It has the basic navigation buttons and 4 dedicated app buttons. The volume controls are on the side of the remote and can be hard to find the first time.

8.0 Remote App
Acts as the Remote
:
Yes
Directly Launches Apps and Inputs
:
Both
Inputs Text in YouTube
:
No
Inputs Text in Netflix
:
Yes
Streams Device Files
:
Yes
Controls TV Settings
:
Some
Voice Control
:
Limited Support

The Roku remote app is very versatile. It acts as a remote, allows you to stream files to the TV, and even allows you to control certain features of the TV with your voice. You can open YouTube or Netflix but you can't search for specific content.

TV Controls

The TV controls are located on the underside in the center of the TV, under the TCL logo and far back. The functionality is limited, and you can only power on or turn off the TV, change input source, and adjust the volume.

In The Box

  • Manual
  • Batteries
  • Remote
  • Composite In Adapter

Misc
Power Consumption : 42 W
Power Consumption (Max) : 73 W
Firmware : 9.0.0 build 4151-30

Differences between Sizes and Variants

We tested the 43" (43S425). For the most part, we expect our review to be valid for the 49" (49S425), 50" (50S425), 55" (55S425), 65" (65S425), and 75" (75S425) versions. 

If someone comes across a different type of panel or if their TCL S425 (4-Series) doesn't correspond to our review, let us know and we will update the review.

Some retailers also sell the S423 and S421. We don't expect any significant differences between the S425, S423, and S421, but there may be some minor cosmetic and technical differences we are not aware of. We have noticed that the specifications for the VESA mount hole pattern on the TCL website for the 65" models are not the same for the S425, the S423, and the S421. As we have only bought the 43" S425, so we can't be sure about those models. If you find any differences in the S423 or S421, please let us know in the discussions down below.  

Size S425 Variant VESA Mount S423 Variant VESA Mount S421 Variant VESA Mount
43" 43S425 100 x 100 43S423 100 x 100 43S421 100 x 100
49" 49S425 200 x 200        
50" 50S425 200 x 200 50S423 200 x 200    
55" 55S425 200 x 200 55S423 200 x 200 55S421 200 x 200
65" 65S425 400 x 200 65S423 200 x 200 65S421 200 x 200
75" 75S425 300 x 300 75S423 300 x 300    

The 43" TCL S425 we tested was manufactured in Jan. 2019.

Compared to other TVs

Top left: TCL S325 (40S325). Bottom left: TCL (43S405). Middle: TCL S425 (43S425). Top right: Vizio  V Series 2019 (V505-G9). Bottom right: Samsung RU7100 (UN55RU7100).  Unlike our other photographs, this picture wasn't taken under a controlled environment, so do not draw conclusions from it.

The TCL S425 is a decent TV that can deliver decent picture quality and is equipped with great smart features. See our recommendations for the best budget TVs and the best smart TVs.

TCL S Series/S405 4k 2018
43" 49" 55" 65"

The TCL S Series S405 4k and the TCL 4 Series S425 have very similar performance. The TCL S425 has marginally higher contrast ratio, which is great for watching movies in a dark room, and a slightly lower input lag, which is good for playing video games. The S405, on the other hand, can remove 24p judder from the native apps.

TCL 5 Series/S517 2018
43" 49" 55" 65"

The TCL 5 Series S517 is a bit better than the TCL 4 Series S425. The S517 can get brighter and is more suitable if you have a bright room; it can display a wider color gamut, which helps HDR performance. Also, the S517 has a motion interpolation feature to please the soap opera effect fans and can display judder-free movies. The TCL S425 has somewhat lower input lag, which is great for video games, and delivers a little crisper motion thanks to the faster response time.

TCL 6 Series/R617 2018
55" 65" 75"

The TCL 6 Series R617 is much better than the TCL 4 Series S425. The TCL R617 has better dark room performance, thanks to its local dimming feature, and better black uniformity. The TCL 6 Series can get brighter and has a better color leading to better HDR performance. The R617 can display judder-free movies, whereas the TCL S425 has a lower input lag, great for games, and a little faster response time, so motion looks slightly crisper.

Samsung RU7100
43" 50" 55" 58" 65" 75"

The Samsung RU7100 is somewhat better than the TCL S425. The Samsung RU7100 can get brighter and is more suitable for a bright room. It also incorporates a motion interpolation feature to please the soap opera effect fans. The TCL S425, on the other hand, can remove 24p judder from native 24p sources and has a faster response time that can deliver a crisper image.

Samsung NU7100
40" 43" 50" 55" 58" 65" 75"

The Samsung NU7100 is a bit better than the TCL 4 Series S425. The Samsung NU7100 can get brighter and is more suitable for a bright room. The NU7100 has slightly better gray uniformity, which can be important to sports fans, and a motion interpolation feature to please the soap opera effect fans. The TCL S425 has a faster response time that delivers crisper motion and handles reflections slightly better, which can be important when you watch TV shows in a brighter room.

Vizio E Series 2018
43" 50" 55" 65" 70" 75"

The Vizio E Series 2018 is better than the TCL S425. The Vizio can get much brighter and has a local dimming feature to improve dark room performance. It also includes an optional black frame insertion feature that can help make motion crisper. The TCL S425 has a lower input lag which is great for playing video games.

LG UK6300
43" 49" 50" 55" 65"

These are two different types of TVs. If you have a bright room with a wide seating arrangement, then the LG UK6300 is a better choice as it can get brighter and has wide viewing angles thanks to its IPS panel. The TCL S425, on the other hand, is more suitable if you watch movies in a dark room and you sit straight in front. The TCL S425 has deeper blacks thanks to the higher native contrast ratio. The LG UK6300 has an optional motion interpolation feature to please soap opera effect fans.

TCL 3 Series/S325 2019
32" 32" 40" 43" 49"

The TCL 4 Series/S425 2019 is much better than the TCL 3 Series S325. The TCL S425 supports HDR and has a better dark room performance, thanks to its higher native contrast ratio. The TCL S425 supports 4k and has a faster response time, which is great for watching sports and playing video games.

Toshiba Fire TV 2019
43" 50" 55"

The TCL 4 Series S425 is better than the Toshiba Fire TV 2019. The S425 has better contrast, a better response time, it can remove judder from some sources, and has significantly lower input lag. The Toshiba is brighter and has an optional motion interpolation feature.

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Conclusion
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7.3 Mixed Usage
The S425 is a decent TV for mixed usage. It has a decent picture quality but can't get very bright, so it is more suitable for dim rooms. It has decent motion handling and a fast response time that leaves only a small blur trail behind fast-moving objects. It has a very low input lag, and it is very responsive, suitable for gaming or use as a PC monitor.
6.4 Movies
This is a mediocre TV for watching movies. The native contrast ratio is excellent, and the TV can display deep blacks in a dark room. Unfortunately, it lacks local dimming to further improve dark room performance, and its black uniformity is just okay. The TV cannot remove 24p judder from all sources, and this might bother movie enthusiasts.
7.0 TV Shows
The TCL 4 Series S425 is a decent TV for watching TV shows. It has good reflection handling, but unfortunately, it can't get very bright to fight glare, so it is more suitable for dim rooms. It has poor viewing angles, and you have to sit straight in front to enjoy the most accurate picture quality. It has decent gray uniformity but lacks motion interpolation to please the soap opera effect fans.
7.1 Sports
The TCL 4-Series is a decent TV for watching sports. It has a fast response time, so fast-moving content has only a small blur trail. It can handle reflections well, but it cannot get bright enough for a bright room. Unfortunately, the viewing angles are poor, and if you're watching a game with a group of friends, those watching from the side will not enjoy the same accurate image as those sitting directly in front. Finally, some sports fans might be bothered by the amount of dirty screen effect this TV has.
8.4 Video Games
The TCL 4-Series is a great TV for playing video games. It has an excellent low input lag, supports most common resolutions, and the response time is fast so fast-moving objects have only a small blur trail. Unfortunately, the TV lacks more advanced features like FreeSync support, that are important to competitive gamers. On the upside, it is a very responsive TV, one of the best in its category.
6.6 HDR Movies
Watching HDR movies on the TCL S425 is decent. The TV has excellent native contrast ratio with deep blacks but lacks a local dimming feature to make dark room performance even better. It can't get bright enough in HDR to deliver HDR content with highlights that pop. Finally, it does not have a wide color gamut, so it can't display a full set of vivid colors to improve HDR performance.
7.9 HDR Gaming
This is a good TV to play HDR games. This is mainly due to the very low input lag that makes it very responsive, and the fast response time that leaves only a small blur trail behind