What's the difference between the rigs with the move.ai_ prefix and all others?

The move.ai_ rigs are scaled to the proportions of the actor, i.e. if the actor's height is 1.8m move.ai_ rig will also be 1.8m in height.

That's the case for all the limbs as well (0.3m move.ai_ rig's forearm length will be equal to the actor's forearm length of 0.3m).