Thanks for the info. Although, in general, I assume a device that allows you to have two-way communications with SAR is preferable even if a PLB might have been better in this ultimately fatal situation.

Yes, two-way communication is a huge benefit since you can explain the problem and the responders can give advice in addition to ETAs.

However, a device like the Garmin inReach requires an active subscription for the SOS to work. If there's a glitch with your credit card and the service becomes inactive while you're on travels, it might not work.

Another difference is that an inReach SOS message goes to the Garmin-run https://www.iercc.com/en-US/about/ rescue coordination center who will the relay to rescue services.

Whereas a PLB or EPIRB communicate with the Cospas-Sarsat system and is handled directly by government rescue agencies (https://www.sarsat.noaa.gov/mission-control-center). While the Garmin service works great, I have more trust in the USMCC being always responsive than any private company.

So the best advise is to have both. I have an EPIRB (for boating) and a couple PLBs in addition the the Garmin inReach. I use the inReach for casual messaging but if I ever have a real emergency I'll activate the PLB and EPIRB first and only afterwards start trying to message via the Garmin.

My understanding is that SARSAT is the only option that has satellites in orbits above LEO, and thus generally better coverage. So if it's down to one thing only, I'd pick the PLB just on the basis that, in a serious emergency, it's more important for help to come at all.