i had this on my M3. It sounds great... sounds very similar to the OEM mod that everyone does, but cleaner sound. The OEM xpipe weight a lot so it is a simple way to reduce some weight off the car.
It is not annoyingly loud, loud when you want it to be - at higher revs.
The only issue I had was with the check engine light. After really hard driving, the light would come on and I would have to reset it.
Endless | Kreissieg | KW | Akrapovic