Both TVs provide decent motion handling, making them suitable for everyday viewing including sports and action content. Both TVs provide standard built-in audio performance suitable for regular usage, though external speakers can enhance the experience. Both TVs come with smart platforms that support popular streaming apps and voice control features. TCL 43S451-CA and TCL 40S5400 differ in resolution (UHD vs 1920 x 1080), which can affect overall clarity and sharpness of the display. Overall, both models are capable choices in their segment, offering a balance between performance, features, and usability. Both TVs offer adequate brightness levels suitable for most indoor lighting conditions. TCL 43S451-CA and TCL 40S5400 are two competitive smart TVs offering a mix of display performance, smart features, and overall value for different types of users. There is a difference in screen size (43 Inch (109.22 cm) vs 40 Inch (102 cm)), and a larger screen generally provides a more immersive viewing experience.

Verdict: Both models offer good value, and the better option depends on your specific requirements and viewing preferences.