It would be interesting to know what they mean by "differential in drums" - it would be possible to really have a center differential, but it would require a drive shaft through one drum to the differential, and probably a concentric bearing to support the drum at the center of the mower. On the face of it, it seems like a natty idea, if you could keep the oil in and the dirt out. However everyone ended up with a pair of sprag clutches instead. Of course they may have been using advertising language when they referred to a differential, and they really meant the usual pair of sprag clutches. A diff is way better when you want to make turns, but not so great if one of the half-drums hits some mud.
