Model A consumes less power than B, because it doesn't have the ethernet chip or port, does not have an onboard USB hub, has a single USB port and has less RAM.

Model A consumes less power than B, because it doesn't have the ethernet chip or port, does not have an onboard USB hub, has a single USB port and has less RAM. A flatter profile is an advantage, when trying to tuck it into those narrow altoid boxes along with other circuits and battery packs.