ORIGINAL: Ing
I've been using K & N filters on my race bikes for years. IMHO nothing filters better. It doesn't get as dirty because all the dirt/sand doesn't fall directly into the filter as it has a top on it. Also, RB Innovations, a major RC supplier sells a K & N filter for their high performance air filter set-ups, only for about $30.
Same here, never had an issue with any 2 strok bikes. 2 things about oiled mesh filters though.
Get a good name brand, lots of knock offs are out there that have a gap of almost twice as many microns as a K&N.
Make sure to clean and oil your filter regularly, If your filter is too dry, it will let dust in. With bikes, we used to do it before EVERY race. Even if you have 2 in a day, we would clean the filters twice. Might seem excessive but better safe than sorry.