Just to share a bit of what little I came across.
Went last evening to friend's house to see his gruppeM fitted on his Honda Accord Euro Type-R.
Its quite cute looking. I was told it can be fitted onto E90 but will likely cost a bit more. he paid $1300 for it on his HONDA.
He also told me he removed a previously fitted MUGEN airbox, bcos the MUGEN cause a dip at the high end, which he didnt like. His MUGEN was only 2 months old, siao ! The GruppeM now gives his car more at the higher end but less at low end. Well it was interesting, I guess at the end of day, there is no free lunch. Turned on his engine, heard the vroom sound of the GruppeM, but was very much drown by the sound of the iVTEC engine.
Lastly gave me a ride at over 100km/h around the narrow streets in his estate, to show me how it all sounds. Its like WRC, my dinner almost kena thrown out.