my 2sen

back in the days, solar film will trap the heat in itself, so when you touch the film, it is hot... you put hand under the film, won't feel the sun, but somehow inside the car got oven feeling

nowadays, solar film technology is super mature, and it's more than just IRR, TSER specs - more important is use few years later it won't have wavy effect

go to shop, ask for house brand, and see if they use it on their own car, and then see got wavy effect or not - look through the windshield, move your head up and down, and see things in distance won't have wavy effect

my personal opinion - don't go brands with branches everywhere
for small sedan, under 500 got many options