Firebase is a great, especially if you want to rapidly develop or test new things. It's saved us days/weeks of time not having to worry about structuring/restructuring our backend and allowing us to focus on getting the UX/design of our app down first.
This has been extremely valuable for our small team -- we've been using Firebase since the beginning and are a big fan of the technology. By abstracting this part of our product away for the short term while we build and iterate, it's probably doubled our productivity - just in the short term, of course (and assuming it would take half of my time/focus to be building/maintaining backend code).
Plus, James and Andrew are always super responsive whenever we bug them for stuff.. they know how to keep their users happy.