Pulling the green "apple" shears off a small diameter tube that has a
closed end. The tube acts as a metering orifice as the bottle
empties. They are intended to feed pressure demand masks after the
mask has been disconnected from the regulator. There is a valve that
closes the end of the mask hose.

I've had one of these on the shelf since I visited the chamber at
Edwards about 25 years ago. If I had ever used it I intended to unscrew
the complete assembly from the bottle and replace it with a reusable
valve. I'd guess it could give a useful duration if connected to an
EDS system.

Mine is still full and likely to stay that way.

Andy