On late model vehicles the front windshield blocks 94% of UVA from the factory wherein the sides (and rear on cars) do not. So you're not really gaining anything in terms of UV protection. You're getting some light reduction of course, but you're also significantly reducing visibility since you have now blocked off the only means of light transmission. Also, HI, OH and ND are the only 2 states that allow tinting more than 6" down from the top and they require 70% light transmission. LEOs usually don't care too much about side/rear tint unless it's below 15% tint, but windshield tint is looked upon very harshly and is almost a certain ticket if you get stopped.