Gator, the RIS rails lock up the same as the Lite Rails. SOLID.

Brent M from DD gave me one of the versions we use on our 10" MK18 uppers. It's so nice.

Emilio, that's pretty much the main reason for the RIS II's design. For installation of a 203. They're nice rails to be sure. In fact, I'm sure your gun would look cool as hell with one on there. Also, you don't have to worry about them coming loose.

Did I mention they are SOLID?

As for the difference in the weight of the two, you're looking at maybe 2-3oz.
Either way you'll be happy with Daniel Defense.