Services/Devices like the Garmin inReach and Zoleo satellite communicators are better than nothing for sure, and a lot of folks have been saved by them, but just keep in mind that the SOS functionality doesn't go directly to emergency responders. Those SOS requests get routed through the services' support center for triage and they will take some time to try and get details about the situation before notifying first responders. That adds time, but also helps ensure the correct responders are activated to help.
With a PLB that's not the case, and I highly recommend having a PLB even if you have a satellite communicator. The PLB signal is generally picked up by the military who then contacts whatever first responders make sense for your location. PLBs are for when it's a matter of life and death. Satellite communicators have a wider variety of situations they can cover but if I had both and someone's life were at risk I would activate the PLB before the satellite communicator.
Another subject that doesn't discussed often enough are the additional costs of being rescued. If you don't have insurance and aren't in a national park (in the US) then you should expect to be handed a bill for all or most of the costs involved in the rescue. Having been rescued in the SoCal desert after breaking my leg 13 years ago I can tell you it's not cheap. The surgery was the cheapest part of that experience. The 90-mile helicopter flight (necessary due to high winds between the desert and San Diego which prevented an ambulance from taking me to UCSD) was billed at over $80,000. Thankfully it was all covered by my health insurance.
So, if you think you could find yourself in a situation where your only option to get out alive is via SOS then I would highly recommend looking into rescue insurance. There are a number of different providers out there and while the cost isn't super cheap it's a lot cheaper than paying for everything out of your own pocket without it.
