Yeah, I'll be the first to admit that this type of lock has some obvious disadvantages. However if you commute every day, there are lots of situations where you have to leave your bike unattended for "just a few seconds" while running errands. The cost of losing my bike for me is bigger than any of the potential problems with the lock.

The most obvious flaw is that is has the potential to damage your components. This really can only happen if someone gets on your bike and tries to ride away with it. It's kind of like choosing between having no bike and a bike with damaged parts. (If you place the lock at the bottom of the chain, you only get a half turn of the cranks which is not that much leverage. Realistically it's not going to do much damage.)

Another flaw is that a theif can just cut the lock with bolt cutters. This requires them to turn the bike upside down- anything that risks attention they might choose to avoid.

Another flaw is that someone can still walk off with the bike. A drive lock at least eliminates the quick getaway- one of the main reasons it's so easy to steal bikes.

And finally if your chain has a MasterLink, they can just disconnect that. This is true, but without a functional chain they still can't ride the bike.

I think it's a good concept- a lock that prevents a bike from being ridden. In Japan, they use the O-lock (which bolts the rear wheel to the seat stays). They do this because there are more bikes than bike parking spaces. Ideally Kryptonite or some other company would make a rectangular shaped drive lock that attaches flush with your chainlinks. No boltcutters could defeat that.

Take care guys.