IMHO "failsafe" thermostat is just a gimmicky marketing terms used, for most of the time when a thermostat fails (and I'll explain a bit more later) by means of remained wide open, your engine will run cool and do not have cabin heat, highway cabin heat is non-existent, radiator runs cool, temperature needle stays at the bottom, etc.
If a thermostat fails shut, you'll see your temp needle creeps up to "H" while your radiator fan (depending on cooling jacket routing and design, some may not turn on the radiator fan) stays on all the time.
I've seen both factory thermostat failed open/failed shut in equal opportunities, and many instances of "failsafe" thermostat failed shut (instead of wide open and locked itself at a predetermined locking tab), causing engine overheating.
So, use it if you will but I wouldn't recommend using them at all (in all my applications and all the vehicles I serviced so far).
Q.