I know I know before you all say it - you don't buy a B5 Tip to improve fuel consumption - far from it really!
But I was just curious (if anyone's actually managed to drive sensibly with one fitted) have you found it uses any more fuel than with a standard airbox? I was thinking (and I may be completely wrong so please correct me if so) that in 'theory' if it's making the turbo more efficient it may even increase MPG if driven off boost... Dunno?!