I drive a 1.6 so the sound is most likely slightly different. So far I'm quite happy with the sound. Not much of a difference while city driving. There's a nice gradual increase in growl as the revs increase. Quieter and smoother than removing the airbox lid. I'd say its just right.
Increase in performance? Meh, I have my doubts.
I'll upload a sound clip tomorrow, but I'm pretty sure it won't be a good representation.