CrDB is not about many many low latency queries, like say MySQL. It's designed more for getting your workload processes down to making as few large queries as every one incurs quorum latencies. You don't want to prototype something in Rails and hope there's no hidden lazy queries happening along the way.

It wouldn't be a good idea to take a large working PostgreSQL app and try to switch over to using CrDB. You'd spend all your time (unwittingly rewriting the entire app) speeding up and grouping a few queries at a time.