Supposedly it is under the best conditions. But like the manual says, it should be changed whenever it gets dusty or dirty. It depends on your environment as to how cost effective the K&N filter will be.

I got mine for about $35 and the recharge kit, which consists of cleaner and oil, is about $15.

Also I wouldn't recommend letting the K&N filter go 100,000 miles even in the best conditions. The maximum, I believe, is 50,000 miles before you're supposed to clean it.

 

I just put one in. Did not notice any difference, but getting more air in to the engine does not happen if you cannot get it out faster. I imagine it should be better with a free flowing exhaust and some programming.

 

I put one in mine noticed little change. Then I moved the intake hose from the inner finder and run it to the front of the motor in the area that you see cold air intakes sucking from and it helped even more. I get about 3 more MPG (if you keep your foot out of it) and fills like it has more torque.