I have a K&N on my '75 Spitfire, but I do not use them on my 'modern' 4-cylinder cars.
I know, I know...there's tons of marketing and 'research' from both camps in terms of particles allowed, etc - but with the tight tolerances of the newer engines, I'd rather stay with the OEM Honda filters to protect my engine.
I don't mind running them on a 30+ year old British engine...heck I think that probably requires some extra particles and dirt - plus I can rebuild that myself if necessary.
This is purely my opinion, I don't have any facts to back it up.