Have you use syncthing with another person? It seems really awesome for me, until I need to add another device, and I can’t imagine doing this with someone not already bought on it. I guess I’m led to think of syncthing as a very personal tool.
At the end of the day, it feels easier to send folks a link to the nextcloud app and they use they’re same login, easy to understand.
But! For us geeks, we should definitely use it more. It fills that same space as sparkleshare, but with less mono.