I use PhotoSync on all my devices and all my family members' devices. I've bought it about 10 times and I'm pretty happy with how it works. There are 2 big features:
1. It syncs to my Nextcloud server which I control. No one can take it away from me.
2. It's not subscription based, so buying it for my parents, siblings, etc. is practical since I'm not saddling them with a subscription they don't want or need.
I think a PhotoSync competitor that's more opinionated (ex: Nextcloud only) with a simpler UI could do well. This Photo Vault app isn't it, at least not for me. I'm not going to pay forever (via subscription) to get less control of my data. No thanks.
I've spent hundreds of dollars buying apps for family members, but I won't spend a penny on anything subscription based. For example, I used to buy Enpass for everyone I know. Then they switched to a subscription model and have gotten $0 from me since.