Well the idea is they plug the box in at home, and the box is the server that contains all their shared data (photos, etc.) and lets them control how it's shared with others. Sure, they can access it from their phone, but the phone wouldn't be the server. The whole idea is that each user has control over their own data, instead of just handing it over to some big tech company.

Ideally no more complicated than setting up their phone and adding personal info/pictures. With an app store that defaults to installing only from official channels but with the ability to add channels more so like linux repos than the google play store.

How many users don't have home internet? You could also pay money for someone else to run it for you and later decide that paying $100 once was better than paying $10 a month forever. Note $10 a month x 5 years = $600.