How is this different to / better than a polyswitch fuse?
Isn't this pretty much how the tried & tested polyswitch fuses work, and I've seen those embedded in battery packs many times.
http://blog.circuitprotection.com/automotive/the-anatomy-of-a-pptc-device-and-why-its-different-than-a-fuse/
They trip with external heat, as well as heat caused by overcurrent.
Maybe the new stuff is cheaper? Still doesn't seem to address within-cell failures, which are the most exciting ones.