My experience with RDS instances that had multi region failover, was that the failovers worked every time we needed them for deployments (I don’t think we ever needed them for RDS failures). The cost though was enormous. Our write db represented the lions share of our AWS cost, and doubling it for disaster mitigation increased our costs by something like 50%. It was mostly worth it from a business perspective when we were less sure about AWS uptimes, but I’m not sure I could keep justifying the cost given how little problems we had with RDS over time.