I once had a K&N drop in filter on an S10 pickup. In all honesty I didn't really notice any difference in performance, and never could get any consistent, measurable mileage gains. It was probably on the truck about a year, the throttle was getting a little sticky, so I pulled the air tube off the throttle body and was surprised at the amount of dust and grit that got through to the clean side of the filter. Cleaned the throttle, dropped a paper filter back in, and never looked back!
It is also telling, that they can usually pick up a K&N filter or a faulty filter in a used oil analysis. The silicon (fine sand particles)levels generally read higher with a K&N filter in use than a paper.
I'm not saying it will instantly ruin your engine or fear mongering. I just don't think it is a wise investment to spend $50 or mor for an air filter that seems to offer no or little measurable advantages in performance, and allows more dirt in your engine.
If you want a good air filter that flows better than stock paper, Amsoil EA filters use synthetic nanofiber technology, it flows better than standard paper and still filters very well.