Totally understand that in theory discs will work better. But having a nasty caustic fluid spill on auto carpet, clothes, hands while transporting is no fun and renders the bike useless. That's my problem with hydraulic discs. Plus hydraulic disks can be hard to keep from running on pads as tolerances are tighter. Again folding bikes have a "jostling" factor via lateral forces that regular bikes don't. And yes I know MTN bikes get jostled plenty but it's more "jolts" than constant pressure from transport.