I'd never touch a K&N oil filter, too many stories of them leaking around the nut and not sealing at the O-ring. I'm referring to K&N oil filters for bikes, but I wouldn't buy them for my car either.
But, like I said, I have had a K&N air filter for every bike I've ever owned, and that's been a ton, dating back to the late 60's. But also, like I said, I wouldn't put on on my Cummins turbo-diesel.