I run a K&N and have had it and my prefilter since 2004. I do my best to wash the pre filter and the k&n twice a year.

 

An outerwear, drycharger or prefilter is always a good idea on an ATV IMO for the extra protection that they offer and I've never had an experience with them hurting power so I always use one on every vehicle that own and race.I've also never had an engine problem that was air filter related in the 18+ years that I've used K&N filters but I clean my filter and outerwear after every race.