Can a chain-lock be better against cutting than a U-lock? I'm looking for a bike lock and, in 2013, Kryptonite have a new lock, the Evolution Series 4 Mini Chain:



The chain is quoted as being only 55 cm long, and 10 mm thick. 

Is the blue mark below a correct interpretation for the reported thickness?





On that note:

To actually manage to remove the lock, would you have to cut through a single link completely in two places? See the red marked below: 



If yes, then that would require cutting through 20 mm of manganese steel — exceeding the 18 mm thickness of the Kryptonite Fahgettaboudit that is often regarded as one of the best D-locks.

So when considering cutting, is the Evolution Mini Chain is actually more secure? (With the added benefit of being more flexible than a D-lock.)



On the other hand, if cut only once, would the chain link bend enough to allow the other to slip through?
As for the Kryptonite, cutting one side an bending is certainly possible, but in reality if you can cut one side, you use the same tools to cut the other. The tools needed to bend the link after cutting one side are almost certainly not portable, and why would you carry two tools when one will do.

In comparison to the D-lock--if you can cut though 18mm, you can cut through 20. It will make no difference. The main difference is a D-lock is susceptible to different tools to a chain. For real security - use both. 

The reality is if they want it, it's theirs, and there's sweet nothing you can do about it. 
The job of your lock is to make your bike less desirable than the one next to it. If you bike is a $10K dream machine, that's going to be a tough job--you will need so much heavy metal it will weight more than the cheapest supermarket hack, and take so long to secure the time saving you get riding it is lost at each end of the journey. If its a $100 hack, then any half decent lock will be good enough.  

The best you can do in reality is "enough to satisfy your insurance company".