I have had mine matched the back which was 15% for me. It's been on there since December with no problems from cops at all. Funny thing is that a lot of people think I'm an unmarked car with the black wheels, tints, and debadged.
i actually just got mine tinted yesterday... 5% over the factory in the rear and 20% on the front 2 windows.... looks great... provides a great ride.. cops actually followed me today but didnt pull me over. ran my plates and kept going. now actually on my previous truck it was a 01 ford escape and it was wrapped in 5% all around.. and never had a problem.. not even a follow..
where about in nc are you, I got 20% just on the fronts thinking maybe going with 50% or so on windshield too. my main concern would be inspection which comes up sometime next year.