It seems like a thief could beat these style of locks in about three seconds with just a crowbar by putting it between lock and rack, on the other side from the bike, and giving it a big twist to pop a rivet. I've been looking for a youtube video of someone doing the same since it seems like an obvious thing to try. But they all seem to be either people showing it off or selling it and if they are attacking it they're doing it with an angle grinder. This BikeRadar article isn't detailed enough to show how they broke it but the damage is about what I'm thinking it would be.