RIght, this version of Apple Satellite SOS doesn't work globally. And clearly, it's not as robust a solution as a dedicated PLB.
That having been said, the best camera is the one you have with you. And while I doubt that many vacation divers carry PLBs, some of them might carry an iPhone in a case for taking pictures. So that's where I see the benefit, assuming that they were diving in an area serviced by this coverage. Not as a replacement for a dedicated PLB for people who actually bring a PLB with them diving.
That having been said, the best camera is the one you have with you. And while I doubt that many vacation divers carry PLBs, some of them might carry an iPhone in a case for taking pictures. So that's where I see the benefit, assuming that they were diving in an area serviced by this coverage. Not as a replacement for a dedicated PLB for people who actually bring a PLB with them diving.