The K&N filter will be fine, I've been running a Vito's filter which is the same as a K&N on my blaster for over 4 years now, and I haven't had any problems due to it not being a foam air filter.
While I do believe that the foam air filters may filter more dirt, there is also the fact that a filter which filters smaller particles will most likely not flow as well either. If its harder for dirt to get through the filter, its gonna be harder for air as well. So as I see it, if a foam air filter is claimed to have better flow than a K&N, it likely won't be filtering out dirt any better than the K&N will.