I have 3 filtered pipes. Two I bought because I liked the shapes and large bowl size and they weren't made non-filter (Stanwell 185 & Savinelli 616), & one Dr Grabow I bought travelling because I needed a pipe, and all Dr Grabow are filtered now (at least the drug store selection).
I smoke them without filters, and they are fine, though the draw is more open. They do take more time to clean though, as I have to swab out the cavern where the filter would go. I've found adapters trap more gunk, so I don't use them.
I doubt I'll get another filtered pipe. I don't see any advantage to them. I've tried them with filters and they just seem to trap and retain the gunk. With a non-filtered pipe I can just swab it out with a pipe cleaner.