To be perfectly honest I don't like the necklace. As a necklace. As an E.D.C. ring its ok and a fair price. But you can do better. In my considered judgement you would do better to put
On a length of cord around your neck:

A ferro rod.
A small Suunto Clipper compass or Silver (Brunton) S.E.R.E 40.
A spark-lite.
Tinder for same in a small capsule.
Whistle and a generic pinch light.
15' cord. Para cord for choice.

Put a signal mirror and other bits in one of these neck pouches with it. Consider it your last ditch under your shirt kit.

Only wire saw on the market worth considering is the B.C.B. They are not brilliant. But they are better than nothing.