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.