Price and Performance comparison

The only thing I have found so far has been from docs, but it is rather lacking in empirical measurements.

My amateur understanding so far is that FaunaDB excels in data models that contain many relations (joins) appropriate for graphs/Neo4j mixed with relations for aggregate computation (PostgreSQL).

So, anyone who migrated to FaunaDB from PostgreSQL specifically - and what was the change in billing/performance when doing so?