This bike lock is simple and easy to use, which is great, because convenience is very important in bike security. If it takes too long to use, then it's not really worth doing.
The unfortunate problem is that the system is poorly designed. The lock slides out of the bracket in only one direction, and on most bikes I'm guessing this is the direction of the horizontal bar. This means that you have to position the lock lower down on the bike, increasing the potential of fouling your feet on it.
The keys are rather flimsy and the flat design means that they don't have much strength along one critical axis. I would be rather worried of breaking one in the lock.
The biggest problem with the lock, however, is that it isn't rain proof. I used it maybe twice this summer in the rain and it is now finished. It was nearly impossible to unlock it.