I'm not a user per se Simon, but I work on the Citus team and can share links to a few customer stories.

+ Implementation of the UK Coronavirus Dashboard running on Citus and Postgres, a post co-authored by the technical lead of the dashboard, Pouria Hadjibagheri: https://www.citusdata.com/blog/2021/12/11/uk-covid-19-dashbo...

+ Architecting petabyte scale analytics using Postgres and Citus, based on an interview with the user, Min Wei: https://www.citusdata.com/blog/2019/12/07/petabyte-scale-ana...

+ Video of a customer talk about scaling a SaaS application on Citus by Jonathan Denney at ConvertFlow: https://youtu.be/PzGNpaGeHE4