Originally Posted by tsl
You want harsh? Step out of Starbucks or wherever and find your bike gone. That's harsh.
The OP demonstrates his lack of knowledge about something as simple and low-tech as chains with his statement:
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.
Um, if it is a master link, wouldn't I just reconnect it and ride off? And if I have to use a chain tool, I carry spare PowerLinks with me at all times. I wouldn't even have to mess around with replacement pins. Under a minute and I own your bike, leaving your cute little lock behind.
Before you accuse the OP of misunderstanding "something as simple and low-tech as chains," you'd do well to understand chains yourself.
If the lock is on the master link, removing the master link would indeed allow the lock to be removed. However, if the lock is on any other link, opening the master link will not allow the lock to be removed - it's still locked to a closed link of the chain. Clearly one would not choose the master link to put the lock through. Last time I checked, there were no master links that magically remove every side plate from the entire chain.
Not that I'm going to start locking my bike this way, for a variety of reasons listed by others. Too easy to cut the lock off, too easy to forget the lock and trash a chainring or a derailleur, too messy to get my hands anywhere near the chain.
If I wanted a small lock that could do this sort of freelocking I'd be inclined to put one of the miniature U-locks around the rear rim, which would prevent it from rotating past the brake caliper. As it is, if I'm going to be near the bike I lock it with a cable, and I don't leave the bike places where I won't be near it.