You own your data in the sense that, unlike services like iCloud, you can mirror all your user accounts and data to your own backend database that you control.

You own your data in the sense that, unlike services like iCloud, you can mirror all your user accounts and data to your own backend database that you control. This extra degree of control, though not absolute, lets you develop your own solution (or integrate someone else's) in parallel should you stop using Simperium. Our libraries are designed to have a small footprint; they're easy to both add and remove. And we plan to open source them in the future. Beyond that, you cite valid concerns for any service.