OP here with an update.

I continue to love my Power2Max; it just works. It's a PITA to replace the battery, but the battery lasts a long time, so that's not so bad.

As a lesson learned, for anyone reading this thread who is contemplating buying a power meter, my wife and I bought a tandem, and wanted power meters. That required getting pedal-based meters (obviously), so we bought Garmin Vector 3S pedals. They work just as well, except (i) the batteries don't last nearly as long, but (ii) the batteries are much easier to change. Had I suspected that I would be buying another bike, a more transferable power meter would have been in order (but the Garmin Vector 2 wasn't very good, so it's not a disaster. But with the Garmin Vector 3 being so good, I'd just get that.