Pretty much if you aren't going to be in dusty areas, then the KN is fine, you can also get a prefilter-outerwear as a bunch of people do and they don't have problems. A lot of people here use Uni though, which is just like stock but allows more air to flow and has a better cage. Just be sure to clean it all the time and oil it properly, no matter what you get.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!