'iball' and Overseer - I've done about 250miles since its been on and I'm still really happy with it.
It doesnt give you a massive power boost at all, but I've found it really helps the car to rev very freely and smoother through the rev range. I'm only talking from a 16v point of view BTW.
The noise isnt intrusive at all when youre driving around 'normaly' you actually dont really notice it. Its only when you want to have a bit of fun you can get it to roar, its enough to put a smile on your face

I'll put some pics up if you want fellas?