I've got the Glock and I've also got the Gerber/Fiskars NATO one. I think the Glock's lock is less solid, although I haven't had any problems -- yet. The shovel is still fairly new. The Gerber/Fiskars NATO shovel is more solid and the locking mechanism is way more solid, but it's too heavy for me to take on all but short hikes. I keep it in the trunk, though, as a just in case.

The lock on the Glock is basically just a knob that you tighten and the friction keeps the spade in place. I don't see it breaking per se, although I suppose you could strip it. It of course could loosen up on ya, perhaps precipitating an injury, but I just check mine every so often, and so far haven't had a problem.