I used on a BMW 3-series (E46) with a twin sport muffler of 70 [mm] each. It was a perfect fit both for the pipes and for the groove in the rear bumper. I just added some HT silicon for a better fitting and to act as glue. The clamp alone seemed to me too weak.
I cannot judge quality as I have them installed only 2 weeks, but in a first glance they look fine.