There's plenty to be said in favour of a combination lock: you don't need to carry a key and it's a neat solution for popping into town. It still has a job to do though, that of keeping your bike safe from nefarious types, and that's where the Abus Tresor falls down: it simply isn't strong enough.
At just over £40 (less online) you'd expect mid-range performance from a U-lock but the Brute proved itself to be a tough cookie and it's a great lock to sling in your bag for the daily commute. You'll need a bag, as there's no bracket supplied, although one is available.
OnGuard's K9 is a lock that promises 'near U-lock security' but fails to deliver in fairly spectacular fashion. It's a neat design and a good option to keep on the bike when you're nipping into the shops – it's more secure than a standard cable lock – but it's not one to rely on for real security.