I had one and it was crap. Even after replacing the studs in the driver's-side manifold, it still leaked. It also rusted faster than anything I have ever seen. It was only on my car for 3 months or so. My UPR X-pipe that I just removed when I went to LT's looked the same as it did when I bought it and it also fit much better. If you are stuck on an H-pipe, try something other than Mac.
I've had mac l/t headers, prochamber, and catbacks on my car for about four months. For the price I paid, I couldn't have a better setup on my car. They sound good - possibly a little more drone than I'd prefer, but not bad - and I've yet to see a spec of rust. Are they as high quality as Bassani? Probably not, but I'd buy them again. Installation was the only negative. I think installation is a pain in the butt with any exhaust system you go with though.
I recently installed the MAC flowpath catback and really enjoy it so far. I still have to figure out how to adjust my tips to fit my cutouts nicely, but the sound is truely unique IMO.
got the prochamber, been on since i got my gt (2 yrs now). this is my overview of it.
pita to install. (but they pretty much all are, not really mac's fault)
fitment is questionable at best, but it will go on there. (def. mac's fault)
will prob. rust quicker than some others, mine has it, just at the welds.
no leaky./ no probs. once u get it on, u can forget about it.
really wakes up the car. was my first mod. & fav. one, besides gears.
sounds bad@ass. haven't heard dr. gas, but this is best mid-pipe i've heard.
between me and a friend we have had around 7-10 mac o/r h pipes and had no problems with any of them. I also got my cobra and it had a mac catback and it sounded pretty good so I kept the muffs when I got my long tubes. I am happy with it and I get tons and tons of thumbs ups.