GCM 2 answered this same question in another thead:
Because this system is considered a "cat back" exhaust, meaning the catalytic converters were retained and only the muffler was changed, there will be no difference in emissions output over the factory system. The reason it's labeled Offroad use only, is the increased decibal output in noise over a factory system. But since the 3.8L and 3.6L engines are relatively small displacement V6's, you have nothing to worry about, they are just not that loud. I run the version of this exhaust for the older 3.8L and really it's how it should have sounded from the factory. It's throaty, but not even close to being obnoxious.
I would add to check your local laws.