We are still measuring how much we are able to optimize Aurora with customers in private beta deployments. Aurora is trickier than RDS because Amazon removed a bunch of config knobs when they rewrote the storage layer. So reducing Aurora costs requires more aggressive tuning strategies (e.g., autovacuum) than RDS, which is why we don't want to just let anybody use it right now. It requires more time on our part to make sure that things go smoothly.

Optimizing MySQL/Postgres RDS in the free version is low risk.