More about the“Ascent” Buoyancy Control Belt for free divers (or Emergency Personnel with no time to suit up fully!) at:
http://www.floridaskindiver.com/BC%20Belt%20home).htm
I spoke with the designer, Chad Carney, this is his website about the device. Decided it was worth getting one for my protection, that of the scooter. Come to find it might even have far more routine advantages in buoyancy shifts in normal scooter free diving. You can even hook up a second stage to it for emergency breathing but that potentially opens a whole can of worms ( potentially nasty injurious even lethal ones too). So, I would think long and hard about even bothering to carry an second stage free diving.
It is an interesting device and perhaps taylor made for scooter free diving, without that exact application in mind.