With today's devices, I think that if a wire is stripped properly, the wire end is STRAIGHT, and the wiring isn't flexed too much while the device is being pushed into the box, they can work successfully. It's when the wires aren't formed proplerly to create an "S" as the device is pushed back that cause problems.
Still, there's too much room for error. The use of these devices requires the installers to be too careful. That's not going to happen in production building.
Perhaps this is the reason these are only ever UL listed for #14, and nothing to do with electrical contact area?
I agree there is too much room for error. It amazes me that, despite the documented problems, stabs are still legal.
