I haven't had the steak sandwich but did have the prime rib sandwich last month, and it was sooooo good! (I heard another guest talking about how good it was as we were waiting to be seated, so decided to try it!).
It's sliced prime rib, very lean (no fat or gristle), piled onto a toasted roll. It's amazingly good. Just as good as the filet I'd planned to have, plus about half the price of the steak!
Give it a try!