Using Stolon for PG is a poor choice. Up until just very recently, they haven't had any significant updates in a year. We've abandoned our use of it in favor of EnterpriseDB.
There's a bunch of our own engineering going into this. But: the good news about this whole situation is, if you have a clustering solution you like better: you can just use it. We "automate" Fly Postgres, but we don't "manage" it. Fly Postgres is using features of Fly.io that are available to anybody's application, not just ours.