@John Hicks if you're assisting disabled turners (which I think is outstanding) I believe that you are right about looking for an articulated arm device, particularly if this is an upper extremity disability. Among the articulated arm devices that are still on the market your pretty much looking at the Yoder Elbo and the Harrison Simple Hollower. Although the Bosch Stabilizer also makes use of an articulation it is really more like the captured bar systems as far as how it is used. If I'm forgetting another available articulated arm, someone remind me.
So looking at these two you shouldn't be too quick to dismiss the Simple Hollower based on it's looks. I have the unit and use it on most every piece I turn, so I can tell you that it is well built and sturdy. Moreover it articulates extremely well and gives excellent tool range of motion, and with one hand operation. It can be used with or without the tailstock and mounted to an outrigger there is enough range of motion to turn the outside of a piece. I use my SHS for most everything I turn, not just hollowing. Here are some pictures of me turning the outside of a piece using the outrigger I made.
You'll notice that I did not turn off the lathe for the pictures. I should have, but didn't. With a little tension on the tool rest the tools are quite stable, which makes them easy to use one handed.
I turned the motor off for that shot, but it's literally that easy to control the tool.
I have seen the Elbo but not had the opportunity to use it. I believe it can be mounted to the lathe bed instead of the tailstock and I think that might lend it to similar flexible mounting. One thing I have noticed about the Elbo is that the arms are short as compared to the limbs of the SHS. This will affect the range of motion that you can get. I'd have to play with one, but I will venture to guess that it would be more difficult to reach around to the outside with the shorter limbs.
I'd love to try a Kobra or Monster, but those are long gone.
I have the simple hollowing system by Harrison specialties. He makes a special version of this tool for disabled veterans. Give him a call, he’s very helpful.
Brandon, do you have any more info about Harrison's "special version"? Be curious to see what modifications he made.