The analog TV signal can not be processed by the Android OS, so the backlight application will not work with regular TV channels. The backlight works only with Android OS applications that do not use protected content. 4K performance depends only on your hardware.
Unfortunately, programs such as YouTube, Prime Video and Netflix use protected content (DRM), so the application has no ability to sync to them. In order to make it work you should use a special client. For example, SmartYouTube.
This item does not work for LG or Samsung TVs because they are not Android system TVs. Please check if your TV can download "Android Ambilight Application" (A paid software) before purchasing.