K&N air filters are supposed to be the ultimate in clean air intake with least restriction, but maybe it depends on your idea of what "ultimate" means. The filter media is composed of multiple layers of cotton gauze rather than fine grain paper, which is why air flows so freely. To make it trap fine dirt particles it has to be oiled with a special tacky filter oil (the red stuff). And they have a million mile warranty, if you follow the maintenance instructions to clean and oil the filters every 50,000 miles under normal conditions, more often with dusty conditions. So far so good, but you need to read the instruction sheet (112-KB pdf file) for cleaning and oiling.
In essence it says to wet the filter element with their special cleaning fluid and let it soak for 10 minutes. Then rinse with water flushing it through from the clean side to the dirty side. So far maybe 15 minutes, but it may be necessary to repeat steps 1 and 2 if it isn't clean after the first pass (maybe another 15 minutes). Then allow the filter to "dry naturally". Well, if there is low humidity that might take another 15 minutes. Then oil the filer element with their special stick oil and allow it to "wick" for 20 minutes. Then touch up any areas that are not a uniform red color (a few minutes perhaps). If you don't have to repeat anything, this process might be done in an hour or so. This doesn't seem so bad if you have something else useful to do for about 45 minutes of that time while it is soaking, drying and wicking.

For those of us who treat the car as a personal hobby, this is called TLC. For those who want to be driving and not tinkering, it may be a PITA. This is why K&N air filters are not used as OEM parts on new cars. Professional service shops are not going to spend that much time for air filter maintenance, and auto manufacturers don't like covering a long term warranty if the car owner might neglect the filter maintenance. Now said, it's your choice.