I have Air80 on mine. it's 80% Ceramic tint.
I didn't do it to make it dark, but it helps block a lot of heat, and that's what I was after.
After years of living in CA and fearing being hassled for ANY tint at all on the sides of all my various vehicles over the year, I stepped up and did it for all the same reasons WhiteExpress stated.
I do not recall the %, but went with the lightest, just to keep the interior cool in the blazing AZ / UT summer desert heat and protect both me and the dash from UV.
The place I went to would only install "Ceramic" Tint on front windows, due to it's higher quality and clarity. You can't even tell I have the full windshield done, and even in low light out here in pitch black nights, it is not a problem.
But, I waited until I knew I would be out here where I live now, where LEO's do not care at all about full tint all the way around, even Limo on the sides.
This is a HUGE difference from CA, where the CHP just loved to issue citations for even the slightest tint on the front sides. Even up in the High Desert community where I lived.
I can understand an "Officer Safety" issue with approaching a Blacked Out car in a big city. But, it is just plain cruel to force people to just sit and bake in the sun out in these harsh desert areas with Insane summer temps.
But, common sense should be used, so you don't push your luck or look suspicious.
In all the time I have had mine done, no one, not even passengers have noticed or commented on the front windshield. And it does work.
MUCH cooler while driving, or especially when entering a vehicle that has been parked out in the sun for a long period of time.
Just get good stuff, like the Ceramic. It is worth it.
*Another tip; If you can get a Doctor's note for skin, eyes, whatever, you can carry that with you and be exempt from most states Tint laws. Present it when stopped. It will more than likely prevent a citation, or if it does get issued, it is a clear cut win in court for you.