I own a DEEPSTAR II. It is a great conversation piece. It is an interesting design. It is different, just to be different. It has a female piston if that makes any sense. The piston is something like Delrin or a similar type of plastic.
The first stage has an un-balanced flow through piston.
One very interesting characteristic is that due to the piston geometry there is no high pressure ports. In the early 1970’s that was the kiss of death. In PR, the SPG was standard equipment by 1971. I don’t remember anyone diving without it, except when I dove my Royal Aqua Master and that is probably the major reason why no one else cared to dive my RAM.
The DEEPSTAR II had 2 low pressure ports, but no high pressure ports.
The regulator first stage works, but it is big heavy and it offer no advantage over a more conventional piston design. Its flow rate is nothing special. The seat is replaceable, but it the piston looks like it will get easily ruined with even small amount of sand.
It is also a very difficult first stage to open. You have to use a strap wrench and the large diameter threads can lock with just a bit of corrosion.
The regulator was a major flop at US Divers.
I like collecting and studying interesting weird experiments like this. Sometimes the design failures have a better story that the successes.