The most noticeable change in aftermarket filters is the engine sound. Also, K&N's sucking of air is better than Simota. I've tried both and I can really observe the difference. K&N responds better the moment I blip the gas pedal.

Your engine breathes better with aftermarket filters. Yeah, it could be true that more dirt enters the manifold, but even with stock filters, there's always a way for all those particles to penetrate. You will just have to change oil a little bit more often.