Love the way it sounds and I know it's good for a few hp. Only complaint is that the tips started to rust on the surface only a few months after I had it installed. I recently gave them a good cleaning to get the rust off with 2 coats of chrome polish and 2 coats of wax. They look brand new now.
Nice and noticible SOTP difference when i had my MAC headers installed, (although i had my x pipe installed at the same time)and i absolutley love the sound, deep and throaty without being obnoxiously loud.
I have a Magnapack cat back, this is a badass system. I also got a prochamber under there and these two combined sound awesome. I have some sound clips if you want. But right now Im in the middle of installing Mac LT's with a Mac o/r h pipe.
MAC has revamped their entire exhaust line for the Mustang. New high temp coating and polished stainless steel, fully adjustable tips! I just put one on Project sub-zero - so look for the article on the homepage of stangnet later this week