Anyone ever use Foam filters instead of k&n's

[stephenpen]

Is it wrong to use a foam filter on a nytro. I was thinking of using the uni foam filters with the k&n prefilter covers.
I don't really see people using the foam filters any more. Everyone is using the k&n style filters. Is it a NO NO to use them on sleds for some reason. They are a third the price of a k&n filter