GruppeM products are typically of the highest end you can find. If you want the best, and are willing to pay for it, they will supply you. Their e46 M3 intake and exhaust system were second to none and looked VERY good while doing it.
The price is steep though. I'll probably be interested in getting their e92 m3 exhaust system before I get the intake. I bet it will sound godly though. So I might have to make some extra room in my m3 planning budget.
I'd possibly be interested in a group buy, but it will have to be months from now since I doubt I'll be one of the first people here to get their M3.