Fitting it on a front windscreen, (windshield) would be illegal in Florida and probably most other states. In Florida, where sun damage is a real challenge, it is illegal to put any film other than one that is FDOT approved on the windshield. And, even the FDOT approved films may not extend more than 4 inches from the top of the windshield. As for the side and rear windows, as long as it does not reduce visible light by more than 35% on front side and 50% on rear and rear side, you can do what you want.
But, remember that while UV is the most damaging, just extreme heat is an issue as well.
I have 35% film on the five windows. It works great and, on my white car, looks great. I had it installed just before the PUB in 2007, and you can see it again when I get there this year. I carry a sunshade to put in the windshield when parked. On a summer day, the shade and tint can make a 35 degree F difference inside.