Interesting that this question came up . A few years ago a friend of mines brother started bashing every air filter that wasnt k&n , saying they were the best since he put one in his 96 z28 . Well we decided to do a little test to see if the K&n was better . Test Bike: ESR trx250r quad (not mine), 1st we made sure that the inside of the carb boot was clean and it was spotless , installed a new uni filter then went riding in a sand pit a few miles away for a couple of hrs . removed the uni and checked carb boot , was still spotless not one grain of sand on the inside . 2nd we installed a brand new k&n with a an outer ware bag over it , went and rode in the same place for the same amount of time brought it back home and pulled the k&n off and holy crap the inside of the carb boot was coated with a thin layer of sand and my buddy was regretting using his $4000 quad to do the test on
. It was pretty clear what filter actually filtered the air better and it was NOT k&n . They are junk , and after that test it proved it . Would never waste my money on one of those pos's.
Opinions are like a-holes but I've seen first hand with my own 2 eyes the difference in an off road application and it was scary to say the least .