I've never heard or seen such a thing stewartb. I'm trying to picture how it works.
Without a hose, could it be pushed open and would it stay open? If so, that thing is dangerous and probably why you don't see them anymore. On the other hand, if those spring fingers had to stay "actuated", and that was the locking mechanism, then that's neat.
One thing that I like about Saf-air over curtis though, is the high drain rate. I use it on my CTLS because of the reservoir location for simple draining, but a curtis is fitted on our warrior because you can wrap safety wire around the hose a few times, put it on, and then "hook" a pigtail of wire over the ears of the valve and it will hold in place.