Are you talking about the engine oil filter (in which case I've never heard of the K&N version) or the panel air filter onto which you put a small amount of special oil? If the latter, in my view they are a complete waste of money and as said above some people believe the oil can contaminate the sensitive probes in the MAF sensor. If oiled-cotton air filters were any good, manufacturers like Ferrari would use them - and they don't - they use paper ones.