i fitted a k+n 57i induction kit to my 20v gti, tbh it was pants......... the mpg went through the roof (due to the k+n oil which is on the mesh on the filter getting on my MAF sensor), the sound didnt suit the car either really, unless you have a loudish exhaust i wouldnt bother, as the noise is not as good as a drilled airbox, any oiled performance induction kits/panel filters can dirty your maf sensor as above and cause excessive fueling/poor running) not straight away but it is known that they can cause problems...
sold my k+n on ebay, now back on standard air box and paper filter...... will get round to drilling it one day when ive got a nice exhaust sorted out..........