My conclusions are that plastic will be difficult to keep clean and free of brace comb, and could be easily damaged beyond repair by vigorous application of the hive tool. You can't blowlamp them either to burn off propolized deposits. Whereas the flat steel ones are relatively heat proof.
There are similar issues with other designs too. When you start to feel resistance to lifting, just slide it to and fro sideways a little to release it from the grip of the wax below.