I think going for a speciality database at this stage is premature optimization. Go with the safe choice (Existing tooling, knowledge, free tiers) and use Postgres or something else established. Later on you can always move workloads to other databases if needed.
It's not really specialized, it's a fancy MySQL until you need more. And then, it becomes 'more' at the click of a button. IMO if I were starting a cheap MySQL-powered project today, I'd use their free tier. The branching stuff is genius, and they're really focused on offering a clean user experience.
