I realize this is an old thread but as it happens, I was discussing this very thing with my mechanic today. I've read about these filters on the forums and was curious. The people backing K&N claim a 3-4 MPG gain in normal driving, and a HP or two gain in more spirited driving. I was also intrigued by the "clean & re-use" aspect of these filters.
My mechanic (Wittler Auto here in Albuquerque) told me that in theory, these filters might be a good idea, but actually, they have a fairly serious drawback. The seal is made of a silicone material, and according to the Wittler, they've seen lots of these filters with deformed seals. Seems that the seals deform when they get hot, i.e. the silicone gets too soft. Thus, when the seal is deformed, unfiltered air gets through to the engine. Thus, they aren't too fond of these things. He did say that *if they were made better* they might be OK. But, they would cost a lot more, too. So, for the time being, I'm skipping them and staying with the standard OEM type filters in my
530.Karl Winkler