We got a couple of these in (the new, metal brackets for the Retinas). It's a step in the right direction in terms of design - much preferred over the whole plastic case. However, the units we received were not good theft deterrents. In short, they break far too easily without requiring any sort of damage to the laptop. My non-expert opinion is that the material is too soft, and that the segment right below the locking slot is too thin.
There does exist the possibility that the units we received were pre-production mock-ups. If that's the case, and I'm just judging the design - shape, installation, use, appearance - I only have positive things to say. But if they ship 'em made out of the same stuff I saw, any thief willing to try to break the device is walking away with a laptop.