I am not a backpacker, so maybe I am missing something but if it is JUST for emergencies what do the Paid services offer than a NOAA Registered PLB Device would not?
As for other things worth paying for: being able to text your family back home and let them know you're running a day late but everything's ok so not to report you as missing goes a long way to helping everyone involved have some peace of mind.
Coordinating pickups and getting weather updates are also big value-adds.
It will definitely be two-way.
If you need the other features then that makes a different argument but the original statement was that iPhone feature would kill these over devices because iPhone could be used to send emergency messages.