Valver has a Mongoose, sounds absolutely wicked.. not at all raspy/Nova ish, just a nice deep tone. Peak noise is pretty low down in the revs, or at full chat, so its quiet on the motorway.
Fitting was done before I bought the car, but I know one of the previous owners (Ben H) had a nightmare with getting it refitted numerous times. It needs doing again now I have the car, as its rattling against the underneath and banging about a bit!