I've used K&N before and sold it off before letting it slowly damage my engine. If you hold it up against background light, you'll see tiny holes in which fine dirt can go through. The size of the particles that can go through it is enough to cause engine harm.

I've switched to regular paper filter as it traps dirt better and did not notice a drop in performance. This is better long term wise in terms of engine health (piston seals etc). Just keep in mind to change it regularly every 20k-30k km.