I had a K&N for several years.
Last time I pulled it off I shined a light down throttle body, and wiped a finger through an obvious trail through the dust on the 'clean' side of the filter.
When I held it upto the sun I saw pinholes of light shining through everywhere.
The K&N lovers either accused me of never cleaning and maintaining it, and others accused me of cleaning it with a wire brush.
Went back to paper, Engine still running, as if that means anything.
Hype. What is the easiest thing one can do themselves for a perceived "improvement", Change the filter.
When spending $$ on something the human wants to see a positive result. If one swears that a new air filter gives them more power and MPG, their Butt Dyno is deceiving them.
The extra flow, if it exists, is only going to be noticeable at higher rpms anyway.
When I went back to paper filters, my Butt dyno gave me that positive feel too. Lying Butt.
BTW their oil filters were once made in the USA. they are now made in Asia somewhere, their efficiency ratings and construction quality tanked.
But they still have that nut on the end, and the K&N name which means so much to so many, but the quality that once existed, flew the coop with the maximum profit, offshore everything, bandwagon.
Much better oil filters exist than K&N if one is paying a premium for an oil filter.