I've had this lock for about 5 years and the best thing about it is that no one has tried to nick my bike! It's an unusual lock and to be honest most thieves will not know how to get round it. Of course all locks can be broken but this one makes life very difficult for the would be thief.
It has to be used properly i.e. make sure one side of the cuffs is locked around your back wheel within the frame of the bike, this protects the bike and also your rear wheel. If the side locked to the bike stand is cut, the thief still has to cut the side wrapped around your rear wheel! A massive dissincetive! The lock affords almost no space for leaverage attacks (the most common way D locks are broken), and it's just too wide for bolt cutters. IT CANNOT BE UNDONE WITH A BIRO!
Like some of the other reviews here I used to struggle to undo the locks and eventually took a really close look at the key and realised it had chipped! I swapped it for another (it comes with 4) and the lock works fine! Yes, it won't fit round a lampost so really only suits the urban cylist where there are lots of bike stands of railings! And yes, like some others have pointed out the carrier is crap and will eventually snap.......I've snapped 2!
Still, with all these problems I'm still giving it 5 stars as it's a great, very strong and lightweight perfect for those quick trips into the supermarket and so far has protected my £800 bike for 5 years and counting!!