Legal in SC is 27% any window except windshield, no tint allowed on windshield except top 6 inches. That being said, they will do whatever you want they just won't put their name on it and you have to pay cash. They do top notch work, I recommend them to anybody that asks.
They did 27% all around (not windshield) on my Si and it is really nice.
They did 20% on the front two windows to match factory privacy glass on my tow rig and its a little dark for me at night. You'll see me with the side Windows down at night to see where I'm turning.
They did 27% on the front windows of my wife's car (which has 20% factory privacy glass on the back) and it looks good.
Others NOT done by Solar Solutions:
I have a friend that did 50% on his windshield. I haven't been in it at night but I think it would be too dark for me. He runs HIDS to make up for it...
I had a friend back in the day that did double layer 5% all around on his S10... Couldn't see a thing out of it... His sister got pulled in it and got out of a fine because she cried to the cop and said it was her brother's.