Scubapro, US Divers, and At-Pack, all had hard shell tank packs, some had internal wing BC and others like the US Divers were mostly cosmetic to capitalize on the Cousteau pack looks. But no one else (that I am aware of) ever made a rigid ballast pack like the Dacor Nautilus.
It is by no means automatic in buoyancy compensation. The diver adjusts the amount of air volume (and water) in the hard shell ballast containers and the only automatic feature is that the air will be added or vented to compensate for pressure changes. It doesnt compensate for buoyancy changes due to the diver wetsuit compression or the tank getting lighter.
I have dove one in the past and it is amusing, but in general not very practical. The only advantage is that if you overweight yourself (for what ever inexcusable reason) you can compensate for the extra weight and the gas volume will stay constant.
I guess it could be a bit handy if you had a lot of neoprene and you were diving at a fairly constant depth were the compression of the neoprene was fairly constant
You not only have to use all the same lead weight to sink the buoyancy of your thermal protection, you are also carrying this small refrigerator size box on your back when you are out of the water and dont forget to empty all the water before you get out.
I have one that I bought used. Some day I will rebuild the air source regulator and the dump valves. I would be amusing diving one again.
If you do a search on VintageScubaSupply.com you will find a lot of information about it... I am sure searat (John C. Ratliff) will post more about it later.