Yes, I did. K&N is in my neck of the woods--Southern California. Several years ago I contacted them about designing a filter for the Jag XKR (supercharged V8). They wanted to use my car for the design work. I agreed and we scheduled a time for me to drop my car off for a few day. A couple of days before I was to drop it off, I informed them that I would be doing before and after dyno testing. (I've been building racing and high performance engines for over 50 years and am obsessive compulsive about testing, especially measuring the final product with carefully controlled dyno tests. My intake and exhaust systems have been developed with many hours of flow bench and dyno tests.) K&N said they would the dyno testing at their facility. I told them that was fine, but I would still be doing my own testing as I have a very solid consistent, replicable, reliable test history on the car. They canceled the appointment the next day, without explanation, only saying that they would contact me in the future if they decided they needed the car. I thought that was an interesting chain of events. I never did hear back from them.
I eventually went to another filter manufacturer that uses a few different types of fliter media, including the oiled cotton type used by K&N (although different from the K&N and demonstrably more efficient and with a higher dirt capacity). I was no longer interested in the OEM panel style filter and needed a cone style filter to fit a new obstruction-free Mass Air Flow sensor (peripheral sensing instead of center post style). This company had some very sophisticated testing equipment and was able to show the differences between the filter media regarding filtering efficiency, dirt capacity, pressure drop, etc. Although their own reusable oiled media was clearly superior to the K&N material in all respects, I, nonetheless, decided the replaceable cellulose media was superior in all respects. The cellulose filters were only marginally less expensive, had higher efficiency from the beginning and held substantially more dirt before air flow through the filter (pressure drop) was compromised.
Although I could see no advantage to the oiled filter media--not to mention the time consumed in cleaning and re-oiling them--I still have have some made to satisfy the demand from those few individuals that believe all the marketing hype and insist upon using them. I've given up trying to confuse them with the facts.
There have been several published tests (just Google) examining the same parameters--air flow (from clean to dirty), dirt capacity, etc., across several brands of automotive air filters. They reveal a surprising range of measurable differences. To briefly summarize the findings; K&N and similar oiled fabric media filters are the worst of the group and offer no flow advantage even when new, they usually have much less surface area (for the same spec filter), and have a much lower efficiency when new. As the "dirt" (a size specific test media) coats the filter, the efficiency increases (of course) and rapidly impacts the air flow negatively. The air flow drops at a much faster rate (less surface area) for the same amount of dirt. This results in a much shorter life cycle between cleanings/replacement.
I have not done this testing, other than witnessing the tests performed by the filter manufacturer I used for my own filters, but have researched it quite a bit and have read several of the aforementioned tests. Those tests were pretty consistent in their results, even with some differences in their methodology. Bottom line: don't believe all the marketing hype, that's all it is, HYPE, not at all based upon demonstrable facts. Yes, K&N and their ilk will keep the cats and dogs out of an engine, but not much else. They yield no advantage over a properly sized (filter media area) filter, capture much less dirt (over a cleaning/replacement cycle), have a much more rapid decline in air flow and a much lower dirt holding capacity (resulting in much shorter cleaning/replacement cycles). This is the synopsis of what I have seen in the tests I have reviewed.
Why waste your time and money in the hopes of (unlikely) obtaining some negligible power increase at the expense of a proven increase in engine wear?