Used four of these with ten Rex’s, a yutyrannus, and three megatheriums for the beta broodmother fight. Went very well as the steggos can knock back waves of araneos at a time, though I do suggest leveling up hit points and melee high before you do.
I think its best use is harvesting berries. It is basically the midgame trike, although i like the trike more with combat. The stego has a slow attack, but is has a large hitrange, and so it harvests lots of berries at once. It also has a decent carrying capacity. I suggest to upgrade weight and melee.