On a TT probably is..
Same with Skylines they are very restricted by standard Air filter and exhaust,
NA is very different to TT,
Same as if you take both cats out of a TT its not as ear deafeningly loud as a NA with boths cats out,
Most of the neg comments on here are from TT owners, not NA owners who actually drive them on a daily basis and can see a benefit or not on "their NA"
As a NA owner who dives one every day i have found the Induction kit to be beneficial to "my car", so really this argument can go on and on ... but "i see benefits" with it on my car ...
My answer would be if you fit one of your NA if you see benefits well and good
if you don't put your Air box back on.. simple
Personally my Air box will not be going back on