Can it even move on regular terrain?
It can move in water hexes only. So it can technically move up and down rivers but its speed makes it cheaper to move soldiers around the map in transport. Basically it is used when there is a considerable approach to the beach and the enemy could fire on them on the way in. Most players when playing beach landing scenarios have the troops deployed on the beach as though they just unloaded from the Higgins. The other issue with using them is the amount of points they cost for units that cannot participate much beyond turn 1 or 2. At least the Amtrac and LVT can function off the beach.