I think a lot what will determine the success (safe) or failure of various rapping styles and devices, is whether or not we are discussing steep angles/slope/spree, vertical, or travel restriction/edge safety.

A Rigger’s belt, ladder belt or other class 1 style harness, might work as a travel restriction, edge safety device or for a low angle rappel. Ideally, they should be under constant tension, as they are not designed to absorb a significant fall, but more to prevent a fall.

Pete