It doesn't sound impressive, it sounds chavvy.
Just my 2p.
May I ask why?
As far as I can tell it's about replacing another known weakness, ie the plastic diaphragm with a metal component that also manages to improve throttle response and reduce lag. Not an issue on the standard tune but somewhat noticeable on a tuned car.
The blurb and GFB website seem to allude to the fact there is no real change in engine sound, this was the main point to my question as I don't want the car doing gay farts everytime I accelerate . I'm guessing that's what you mean by chavvy, and I couldn't agree more.
I did notice they have recently redesigned the unit due to leakages, so perhaps it's not sorted yet, still if it improves the viability of my engine componants especially in the improved tuned state, then I wonder if I might just try it anyway. Maybe slightly paranoid since the engine issue

Sandy