As a fellow designer, I understand what you are saying. The gruppeM is overpriced, but that being said, it is what it is. I dont think its worth even 900, but its a japanese part, and japanese stuff in low production is very expensive. People it seems are getting cheaper and cheaper, and it really pushes the quality of all aftermarket stuff down.
How does the GruppeM sound on the 335? Can you hear the turbos?