i had the K&N on my Racing Beat "cold air" intake for my heavily modified Miata. The intake was awesome for the money spent. Great sound and a marginal increase in power. Not bad. The problem was that whenever I removed the filter to clean it, the thing was just filthy. the sink in my garage was full of grit, sand and all manner of debris. I'm not really sure what it was filtering! large birds? great.... I have to think that much of that was making its way past the filter.
Not doing that with the Boxster I thought.
I use the the Mahle from PAP-Parts or Autohauz. I don't see a reason not to.