I only have about a month experience but the real issue is you have to do a lot of things manually that are done automatically in other systems like Cassandra.

Particularly rollups and stream like things. That is you have to do the rollups (as well stream like things) either through postgres rules,triggers Listen/Notify, cron etc. With system like Druid (Cassandra), Elastic Search and other time series databases this is not needed (either the query ability is efficient enough because of compressed or it is automatically indexed or both).

For the stream like stuff we have been using Pipelinedb. Pipelinedb is annoying though in that it is a fork and not an extension. Pipelinedb has a similar problem. You have to create the streams apriori.

So both for Citus and Pipelinedb you have to do some planning of your schema where as the other guys you can do more exploratory/adhoc analysis and queries. The disadvantage to the NoSQL guys (besides maturity and literally no SQL) is that you pay a lot more in memory as most of them (IMO cheat) and rely heavily on available memory. Postgres is very memory friendly.