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http://www.kabrus.co.uk/
I have the small one of these. Keys > combis.. -
Just don't shuffle tumblers too much, I just move one tumbler by a couple of clicks. One by a single click and leave one in the correct position to unlock it. Odds are that if someone tampers with it the first thing they will do is lock the final tumbler. If someone wants to rob your bike they will just cut the cable so having the tumblers well shuffled is pointless.
I bought mine a few years ago, it's the same as the one in the photo but with a yellow sticker. There's a couple of other more expensive options, beware not all that look like this are alarmed. I definitely rate a combination lock as well, no keys to worry about.
http://www.racking2go.co.uk/mini-lock-alarm.html?gclid=CMSrgOyqwcsCFUSVGwodaz0KEw