What would you do if you happened to be under some kind of overhead restriction? E.g. in a simple swimthrough? In a shipping channel where you have been told not to shoot an SMB? I dived with that restriction in the Saint Lawrence River. Getting dragged by a 400' cargo ship doesn't sound fun (but, being on the bottom and listening to one go by overhead was really cool!). Nor does plunging to the bottom because you were using your redundant buoyancy and a ship ran over it and trashed it. And what do you do if you shoot your redundant buoyancy to the surface and there is surface or midwater current that is trying to drag it away from the anchor line you need to get to?
When I took Solo Diver, my instructor showed me how to use a lift bag for redundant buoyancy and had me practice it. The method was to clip a lift bag directly to my scooter ring and sort of lay on top of it. It really wasn't that difficult. Another instructor I've trained with teaches to clip the bag to a D-ring on the shoulder strap. Similar idea but I like the scooter ring deal better. No contortions required to reach the bag's dump valve when needed, and the lift is not pulling you out of trim to one side.
Really interesting discussing, keep it going. I've read it before but this sounds like the Self Reliant/Solo diver course is really a great course, even if you don't plan on diving solo.