We also use RDS in Zalando (and it works great!). With running Patroni on Kubernetes we get several benefits over RDS which in our opinion warrant the effort. Some examples include:

* Real superuser access to the cluster

* Installing custom PostgreSQL extensions not available on RDS, PgQ (Queues in PostgreSQL), PgDecode (logical decode to Kafka/Json), PgJobs (minimalistic jobs in PostgreSQL)

* Easier migrations via S3/Streaming replication from and to AWS - RDS currently offers no way out of RDS to another PostgreSQL cluster

* Deployment model allows for more availability/flexibility with less costs - EBS + S3 allow us to run single node PostgreSQL with high uptime

* Multi node PostgreSQL can run on different node types

* OAuth login for PostgreSQL (via PAM)