The oil from a K&N will mess up the AFM. The AFM (air flow meter) reads how much air is going into the engine. The oil gets on the sensor and gives a wrong reading, and you can not clean the sensor because that will mess it up too. Some people have problems with this and others don't.
"ao ia it worth it" (as in the apexi- no oil) IMO yes.
"ao ia it worth it" (as in the apexi- no oil) IMO yes.