Okay, I put the K&M air filter into my 2014 WRX Limited. I have been cleaning it as per manufacturer recommendations. Frankly, I wasn't expecting any real noticeable gains with it (and liked the idea of a reusable filter that would generate less waste). But I have to admit, it's a bit of a pain-in-the-ass to clean the filter properly. It also requires a fair amount of time and patience to do what would otherwise take 30 seconds.
I am thinking of ditching it and going back to paper...
PS: The car is chipped and modded with an NVidia downpipe, Greenspoon adaptor and a Maddad 3" exhaust. It is sweetly tuned as well.