I have the Supersprint Magnums on my M5. We installed them day one when I took delivery. Therefore, they have gotten a little louder since the first day, as I now have 3900 miles on my car. I really like the look. The tips are larger and more pronounced than stock and additionally, they are chrome plated. They also sound great.. especially when you step on the throttle...nice deep rumble, but not obnoxious. We would not want this car to sound too loud?...
I put the B&B on myself. There were a few quality issues, and as I understand it, B&B is mailing me a replacement.
These pipes are loud under 2500 rpm, sound is great. Above 2500 they get quiet quickly and at freeway speeds you can hardly hear them. Makes matching engine/road speeds much easier on downshifts as you can actually hear what's going on.
I haven't heard the Dinans yet but I am sure they are as good if not better, given the companys reputation.