I ride in extremely dusty/dirty conditions with a K&N clamp on, no lid, & an Outerwears; if oiled correctly a K&N does just fine at stopping debris from entering your motor. They offer the best gain and I have been running one since 2001 with no problems. When I upgraded my piston from stock there was no evidence indicating anything abnormal entering the motor...
When the sun is shining here the dirt turns into a fine powder getting kicked up in the air by the tires making it so dusty that it's hard to see a few feet in front of you very frequently (and if you don't have goggles your eyes get gunked to ****); this is a good test and proof enough for me. The task of cleaning a K&N isn't hard at all - you buy a recharger kit that comes with cleaner and spray on oil, they cost 9$, do multiple cleanings, and are readily available at your local Walmart, Auto Supplies store, or dealer.