The general consensus is it doesn't really do much tbh, if anything you can hear the intake more and turbo more on the 2.0T and the CDTi's. Its more of a placebo affect. You'll still notice the air filter gets dirty on one side so the flow is still following the same path.
What does work however is a K&N panel filter. Again I wont say it'll give you any more power as such but it does give a far better throttle response. I never really noticed the K&N until I put a fresh factory one back in and all of a sudden it just felt flat to drive.