I spent a while looking around for a bike lock to secure my bike in central London and finally settled on buying this, as a lot of the advice recommended using two different types of lock. The D lock provided feels very sturdy, but is so small that in practice you can either lock your wheel to the frame of your bike (and not the bike rack/post), or lock the wheel to the bike rack/post (and not the frame of the bike) - what I really want is to be able to secure a wheel to the frame and to the rack/post but you can't do that with this lock. The extension cable that comes with the lock is useful for securing around another wheel or part of the bike frame, but I soon realised that all the thief would need to do is cut the D lock and the extension cable would come lose anyway. Finally, on a couple of occasions since I got this lock a month or so back I have also had problems unlocking the D lock and have had to spend 5-10 minutes jiggling the key about (and cursing) to make it open. Not ideal. I am still using the lock, but think in practice I'll need to buy another lock to be really sure my bike is safe.