I use
this, lock and chain, when I have to leave the bike unattended. I doubt that it can be cut with a 4-foot bolt cutter (chain is hardened as much or more than cutting blades). Sure it can be cut with a grinder but without a way to hold it, it would be risky trying to. In a vise, yes, but in the field you need to secure it, or you risk injury when the cutting disk jams and flies apart. It weighs the same or less than a U-lock, and it is easier to secure to wider items like poles.