Oh yeah, the absolutely do not recommend using the filter with MDF. They estimate ~200 cuts on ply vs ~1400 on hardwood, and straight MDF would be even worse than ply since the entire width is MDF rather than being sandwiched in veneer.
Presuming you have to use a filter, you’ll need to order a refill. Once you have it I’d strongly suggest attempting to clean the old one, and looking into installing a pre-filter for the future which should help increase your filter’s life.