Film performance deteriorate over time. Cheap one lasted probably 2 years, then no more effective. Branded one maybe longer a bit like 5 years.

The warranty is usually it is not bubbling, de-laminating, wavering, etc; but nothing specified on TSER, IR, whatever

So, you can choose cheap one and replace every 2 years or expensive one replace every 5 years. Normally once installed, people forget about it.

SunCool? I think it is China made own brand? Use same style like SunGard but probably not related at all.

Many brands usually own by a big company like Maduro. Solutia is the biggest tint film maker in the world. Some example here. You can click and see what brand owned by what company.

https://tintindustry.com/window-tint-brands.html