"Quality" can mean a lot of things. There are two basic concepts with air filters. Your common paper filter uses a thicker filter element. It looks like a really miniscule screen door, to use a wierd analogy. K&N's and other "high flow" filters use a different concept. They have a much "looser" filter element with a lot more space in between fibers. But they are also a wet (oiled) filter. So the air within that thin filter membrane gets "bounced around" (again using laymen's terms) a lot more. As particles in the air are moved around, they come into contact with oil-covered element strands, which trap the pollutants.
The difference is by allowing more cubic ft of air through per second, they are allowing more airflow to the engine, while not sacrificing filtration ability.
Superflow, K&N, Tochu, all the true high-flow filters work on the same principle. Whether each has the same effective filtration capabilities is unknown outside of testing. The highest flow "filter" would have one strand of twine across an empty hole. Sure, it allows a lot of air in, but isnt catching much. Look to consumer testing for comparison. HP gain wise, dont expect anything noticeable swtiching to K&N though. You are barely getting anything as it is from that Ractive intake. Worry more about filtration capabilities.
