Doesn’t answer your question, but here’s a quote from the Pragmasis website (www.securityforbikes.com):
Use a good-quality chain and lock or D-lock!
Use the best security you can afford. Don’t secure a £2,000 bicycle with a £20 lock!
Police guidelines are to spend 10-15% of the value of the item on its security. This is a simple statement that can become inappropriate at the extremes, but it gives you an idea of what might be appropriate if you know the value of your bike.
Try to avoid using cable locks altogether as virtually all of them are very poor as deterrents. There are several ways these can be attacked, not least with cable cutters(!), but hacksaws and wire-cutters etc will often only take just seconds to get through cables.
So if your bike is worth £200-300 then go for the <£20 lock….