@KolokokoBird @briar The eternal problem, yes. To be sure, none of these have the polish of Signal (which has integrated video calling, photo attachments, etc) so getting non-techies to use them day-to-day may be a challenge.
And yet, there was a time when I was the only one I knew using Signal, and now my contact list there is full.
In any case, you could make a STRONG case for this when going to a concert, festival, campsite, etc. "Works when cell is unavailable"