Gandalf-the-Diver
Contributor
The pony is there for when your out of air regardless of the reason, if it's stupidity it should be corrected, but the pony is for when you run out of air.
The agencies teach NDL buddy diving, and if done properly there is no need for a pony.
In the 1980 PADI OW manual, the pony was discussed, as was the alternate second, as safety equipment for divers. The class was taught with a single second stage as was the norm at that time. I picked up an alternate second within the following year. I don't know if they still cover the alternative now.
PADI OW e-learning covers pony bottles ... for about 15 seconds