Valve stems don't normally fail suddenly and leave you stranded unless you are off road
it happened from time to time when I used to 4wheel jeeps. your rim hits a rock or log, especially in a muddy rut and rips the stem clean off
so it's rare on the road but it if happens you're screwed.
normally you need to break and re-seal the bead to replace a stem, not something easy to do on the shoulder of road or a trail
small trailer, golf cart, lawn mower tires can be a bear to set the bead
so this might not be for everyone
it's pricey, but could save your bacon in a pinch
I ordered one for the toolbox in my truck to go with my tire plug kit
