Olly, we've all been there before mate (well, maybe not with the supercharger air-filter thingy though ;) :D ). You're not the first person to be sucked in by sales shpiel, and you defo won't be the last.
The great thing with this club though, is that if you ask & take in the advice given, you'll save hundreds, if not thousands, of pounds when it comes to tuning your motor.