I don't see this being a great idea for us urban commuters although I understand Halo's scenarios for its use. I would hesitate to rely on a padlock that was thin enough to fit through the chain since it is so easy to cut with a large pliers or very small bolt cutter. Even as an extra deterrent in the commuting scenario it wouldn't be that great.

I looked at it and thought it might be a good idea for bike tourists who don't want to carry full U-locks. If I were to use it while touring I would use a little larger padlock that I could run through the bottom of 1 or 2 chainrings and hence around the chain. That would certainly stop a ride off, but it would not stop someone walking off with the bike or tossing it in the back of a truck. Again I would not use it in an urban center but if I wanted to stop for a short bit, it might be a decent idea in conjunction with a light cable lock.