Not many around here that I know of .... they are too short for those after performance, too noisy for home owners and too ugly for me. LOL (actually those are all MY reasons for not trying them)
They aren't talked about here much, but I'm sure someone has tried them.
I can dig through the dyno files, i know I tuned a R3 with them.
Off the top of my head I remember them being RASPY and not performing as well as expected. But I could be mis-remembering.