The cases are tiny, but fit loads! My local GW was playing with their delivery this lunchtime, and they fit the entire contents of Dark Vengeance into half of the Skirmish case (one of the two trays). To say that I'm impressed is an understatement! If you don't have tanks/fliers/knights, a Skirmish case is all you need to carry an army.
I don't like the look of the Battle case, it's dimensions just seem off to me. Looks too short & stout, like a lunchbox or something. I'll probably get a Crusade and a Skirmish.