I don't think Rapp is the last S the Rams will grab and I don't think he's going to really play a Safety role.
Rapp is slightly shorter and lighter in weight than Barron, But he's going to put on 7-10 pounds most likely within his first 2 years in the NFL.
Neither of them is extremely fast with straight-line speed, but both play fast. Both will "Thump" you if given the chance. Both are solid blitzers and can cover RB & TE.
He's a bit of a defensive swiss army knife. I like the pick because they get a younger, cheaper version of Barron, but I don't love it. Hope McSnead can get me to love the pick in a year or two.