Interesting - I do wonder how well that attack would work in a normal use setting where it could become much harder to brace the lock against something.
He's got a couple of videos using it in different ways and it doesn't look like it would be too difficult to brace a lock in some way to use it, like using the tension in the chain or hasp it hangs from. But you're right, in some circumstances it probably would work. Seems dangerous though, both in debris flying off and even more so since it looks like a gun.
I suspect you can find a way to brace them in many circumstances, some of the common bicycle theft techniques are pretty constrained. The down side of this method for a thief is that they look very much like a handgun for obvious reasons. That ups the chance that a quick theft escalates to gunfire if you're interrupted by the police, armed security, or an armed home owner or bystander. Cops are a lot more likely to shoot you if they think they saw a gun.