I think everything got started on the race track where losing a wheel was a real disaster. They started with the type that required a ring to be welded onto the snout of the brake hub and evolved to the clips that bolt to the wheel cylinder. I don't know if the later type is approved fort use in the vintage racing circles (anybody?).
Remember that these clips are designed to get you to the edge of the highway, not to hold the wheel on when you are being towed home. You are probably not going to be making a lot of sharp turns getting to the edge of the highway so the drum will not try to walk off.
Any car I have with hydraulic brakes has some sort of retainer. I wish there was something made for the mechanical brakes.
Charlie Stephens