I would go with a disc rohloff in a heartbeat for my MTB if I wanted gears. the only drawback it seems is that there is quite a bit of inefficiency at high gears (granny gearing10-14) from what I hear (despite what rohloff actually reports). It weighs a ton also, but like others have said probably not that much more in the grand scheme of things after you account for the other bits you don't need.