Crazy but aren't these just props?

Nope. Most of the guns in that box are Harlot derringers with a few Liberators. Neither design is one I'd fire without carefully counting my fingers after each shot, but they do work.

Let's chamber a round and see.

It seems to depend on what ATF regulation you want to look at. A lower receiver, according to the ATF, is a firearm and needs to be regulated.

What these gun buyback stunts have further illustrated is just how much of a patch work mess the gun laws have become.