I haven't had any problems so far with aspen, but I also feed in a separate tub, at least for Deejay. Stitch is still more comfortable feeding in his own little house, but I put his food on a plastic lid, and watch him like a hawk while he's eating to make sure he doesn't swallow any aspen.
They don't usually just ingest the substrate during their regular activities, do they?? That's something I kind of wondered about; if burrowing around, they would end up swallowing some? Then I would definitely look to another alternative.