Citus works really well *if* you have your schema well defined and slightly denormalized (meaning you have the shard key materialized on every table), and you ensure you're always joining on that as part of querying. For a lot of existing applications that were not designed with this in mind if can be several months of database and application code changes to get things into shape to work with Citus.

If you're designing from scratch and make it worth with Citus then (specifically for a multi-tenant/SaaS sharded app) it can make scaling seem a bit magical.