I only use them on my highly modified toys, I don't like the maintenance on the daily stuff vs regular paper filters (cleaning/oiling/flipping, then the additional mess they tend to make on the MAF and throttle body and intake walls). One less thing to worry about. And with the modified toys it's more of a packaging issue (I don't want to fabricate a sheet metal air filter housing to use a panel filter vs just slapping a cone on a 4" tube). IMHO the extra cost of the K&N vs a normal maintenance schedule with paper WIX brand filters is a moot point as well. It's really more of a break-even and I think if people did the math they actually spend more on a K&N over a 100,000 mile ownership period. Replacement Napa Gold paper panel filters are like $10-13 typically, a K&N panel is typically around $60 but even if you shop around and find one for $45, that's 3-4 filter replacements. Mileage improvement for cotton vs paper element filters for the same design is pretty moot, same with power improvements. Third parties have done flow tests on them on considerably higher output engines and it's minimal, translate it down to the displacement and output we are talking about here and it's even less. They are really more about sound and the psychological effect. When you change the intake design you can start to notice subtle differences depending on what you are doing but again it is very minimal. Still they are an inexpensive and low skill modification which makes them popular, well that combined with the tremendous marketing machine behind it.