I didn't go for it but wondered how good or bad it really is.
Good for you.
How good is it? Bad. Really bad. Really REALLY bad.
If you're more bored than I am right now try looking up the pressure differential necessary to rupture the lungs. If I recall correctly it is less than 10 p.s.i. That's well and truly under the 135 p.s.i. available unregulated through the lp hose.
An ordinary second stage requires the OOA diver to stick it in his mouth and breathe. No special training required. In order to use this widget safely your buddy must be familiar with the special technique for breathing it without risking a lung overpressurization injury. Of course, divers and buddies
always remember to review equipment quirks and do an air share drill immediately before descent.
What happens if you are diving with a group and the OOA diver isn't your buddy and hasn't been briefed on this gadget when you hand it off. Confusion can kill in an emergency.
My first BCD was the first model of a USD horse collar to be equipped with a power inflator. Unlike today's models the lp hose connection was male instead of female and had the Shraeder valve exposed on the end. When disconnected from the vest you could operate the Shraeder valve with your finger and breathe directly off the hose. However, as with breathing directly off a cylinder valve, you had to be very careful to keep your mouth open and bubble the air into it, else risk blowing your lungs out.
A parlour trick for the young and stupid, not something for an emergency. Of course, maybe I've missed some recent advances in physiology and breathing directly off a 135 p.s.i. supply is now considered safe.