First, I'm most impressed with the fact that this bolted on and "just worked" perfectly with the ZZP 3" downpipe. I've dealt with aftermarket exhaust systems before and frequently there's something that leaks or needs to be bent into shape or rubs on the car or some other needless problem. I am happy to say that this exhaust exhibits none of that. Everything bolted up nicely and while the tip was a little big and show off-y, I've grown to like it. I've had it on the car for a couple of weeks now and in general, I do like the sound. There is NO awful 3800 rasp to speak of and the tone is very mellow, BUT there is an appreciable amount of highway drone. It's not awful, and it's certainly better than many other 3800 exhausts I've heard on Grand Prixs, but it's something to be aware of. Otherwise, I have gotten compliments from people on the sound.
It also appears that at some point, ZZP stopped using a Magnaflow muffler. This has some "ZZP" branded muffler, I have no idea who makes it, but it is a straight through design that seems to be a generic MF clone. They really need to edit the item description.
A final note is to NOT use the included gasket. Unlike the very nice band clamps they include, the gasket is hot garbage. Throw it away and buy the Remflex 8038 kit, which comes with two 3" gaskets, which I used for both the rear Plog to DP and DP to exhaust flanges. Aside from those minor complaints, I am VERY happy with the exhaust and I'd much rather bolt this on in my driveway than go to an exhaust shop.