5% is very hard to see out of at night and is dangerous to put on front windows. Where I live the limit is 50%, and that's only for passenger windows and the rear window. There's a 2.5% tint out there also. 20% is only legal in a few states. Southern states are the most forgiving due to the hot sun heating up your cars interior.

Window tint is very easy to remove. If you happen to get pulled over and the police men tests the tint with a light gun and you fail, in some cases he will make you peel it off before you can move your vehicle and may give you a fine. There used to be a spray on tint but I don't know what happened to that. The film is a pain to install.