The behavior of the RedPower Filter when pulling from an inventory and given a filter list was to eject only the items specified in the filter and only in the quantities specified. The Fitlered Importer seems to eject an entire stack regardless of the amount specified in the filter set.

I'm not entirely sure, but I believe it would also restrict the amount that could be sent to it through a pneumatic network in a similar fashion, though I never used them that way myself.

Unsure if this is a feature or a 'bug', @MrTJP?