[soutthpaw]

Well as you already know my thoughts, They suck for modern electronic controlled gasoline engines for the simple fact that the oil seeps off the filter into the intake and attaches itself to various sensors. The thin wire or wire grid used in MAF sensor gets covered in oil and dirt and gives false readings... thus the output of the engine is only as good as the data coming into it.. A bad or fouled MAF sensor can result in poor economy, fouled plugs, carbon buildup etc...
They are fine for carbureted engines as these don't have the electronic sensor to foul up and don't use a computer to control engine operation.
As for K&N they just let too much junk through. having seen the intakes of many vehicles running K&N as well as owning a couple of vehicles that had them when I bought them I am convinced they let too much stuff in ... I could actually see right through one of them the spaces between the weave were so big....
As for small engines, That was my specialty when I worked for a John Deere dealership for a couple of years.... I have never seen such neglected equipment in my life! people buy this stuff and just run it till it dies with ZERO service or maintanence and then bring it in when it quits running... Stale, untreated fuel and 2 stroke equipment that did not have the oil added to the gasoline were the 2 most common issues... along with mower blades worn down to nubs of steel..... again these air filters would have a half inch thick layer of dirt and debris on them so oil what not even the issue... John Deere also changed it recommendation for many of the filters that required oil and now say don't oil them....