Over a standard setup with no cold air feed I might be inclined to agree with you that there will be a small (very small) bhp improvement, but it has been tested over and over, with various different setups over on clubgti (with back to back dyno plots) that the best setup is still the factory airbox, modded, with cold air feed and aftermarket filter. My arse dyno would also disagree with you, there is just no way that that setup produces more torque or power. I spent money on mine and trust me, I didnt willingly strip it all back off again after less than a week. It is now sitting in a useless heap in my garage, it made my car gutless, when she is normally anything but.
But, if you like it, then stick with it, all I'm saying is that there is evidence out there that contradicts it.