In North Carolina, unless the law has changed, its not the specific muffler, its the noise level, they can write you a ticket with a stock exhaust system, its called "excessive noise", that is what they get you for, not your type of muffler or exhaust system, you can have anything you want, hehehe.
In NH, you're not allowed to have an exhaust that's louder than stock. The only time I've heard of it being enforced was when Portsmouth set up a day to bust people with loud exhaust; they caught mostly Harleys. It was announced the day before, and reported the day after in the news.
I cannot say are the thrush mufflers we talking about cherry bomb style or like a typical turbo muffler like this. If we are talking about chery bomb style it will be loud. the only thing louder is open pipes with no muffler at all. If we are talking about a Thrush turbo muffler they will sound very good and at a nice price!!!!!!