Went to the Toyota dealership to get some parts for work, and to check on some things for myself; Guess what they had on the parts section shelf? The K&N golf ball display that totes how good the k&N filter is. I told the kid I wouldn't think a Dealership would promote an aftermarket product such as that, as the engineers do a lot of research in designing a car. He replied something to the effect that the engineers are bean counters and that on some areas they cut corners to make something cheaper. I told him of the Filter study done and it's results, but he seemed to think it was all internet garbage. I also pointed out the push for Genuine Toyota Parts on a Toyota Car, and how something like a MAF has difference specs for each car, that a aftermarket brand won't always have the desired results. In our shop we weigh the cost vs. availability and performance of such parts on a daily basis. Most of the time OEM looses over cost; but if the Dealership doesn't stick with OEM parts, why should we.
A instructor told us at a class "If the aftermarket parts world worked (such as performance air filters, fuel line magnets and such) the car dealerships and designers would use them, for in the dog eat dog word of cars every MPG and HP is a selling point.
I have a K&N in my truck, I fell for the Hype years ago. Someday I will replace it, but after reading the filter study I'll never own another one.