I got one as a gift from my old LBS when we made a big family move (as an aside, you know things have gone to far when your LBS owner is a floods of tears when you leave… Oops!).
My experience was that it registered a crash pretty well, and then my phone would start howling at me as it gives a few-second warning before it starts calling your wife, ambulance service, the police, the UN Security Council, MSF etc etc.
Unfortunately it also thought I’d crashed every time i landed a drop like a sack of tattles.
There was also weirdness with it only working (or ‘on’) when you connected it to the Specialized app, which you then had to use to track your ride. Not sure this is still the case, but it felt a lot like nothing to do with my safety, and everything to do with Specilized harvesting data. There was general faff with shoogling helmet to wake it up, connect to phone etc.
Used it a few times, though ‘huh, could be useful’ then got annoyed with the faff and never used it once the battery ran out (which didn’t take very long.
HTH.