The Monster Mill (two roller) only has one roller actively driven by what you run it with (drill, motor, hand crank)... IME, the MM2-2.0 doesn't need to have gears to drive the second roller. I've run a good amount of grain through mine (been using it about a year now) and have not had any issues with it (at all). The longer, larger, rollers put the BC to shame. Even the base MM2 model has larger, longer, rollers than the BC (6" long, 1.5" diameter).
I had a BC as my first mill. I quickly got tired of the small hopper (could only get the 7# hopper due to what was available when I needed it). When I had the BC, you could NOT get the extension for the hopper from BC. You couldn't even get just the hopper by itself if you wanted to (poor practices IMO). So, I went to Monster and got my MM2-2.0 with base, hopper and hopper extension. I can now mill up to about 39# of grain at a single time (no more refilling the hopper). The most I've loaded it up with, so far, is 30# of grain.
IMO, upgrade from your little [girly] BC mill and get a MONSTER! I don't regret (for a nanosecond) getting the MM2-2.0 (BTW, with the hardened steel rollers, so they could probably mill a person and laugh at me). If I could do it all over again, I would have skipped over getting the BC and gone directly to the Monster... :rockin: