Craig from Citus here. Thanks for the kind words. We've seen a lot of people scale-out transactional workloads with Citus as well. In particular, we've seen a lot of multi-tenant apps that need to keep scaling beyond a single node when they're running into memory or compute issues.
If you are looking for something that is more Postgres flavored (meaning we're just an extension to it so you get all the good stuff of Postgres such as JSONB, PostGIS, etc.) then we hope we'd be a good fit. And we run a managed service on top of AWS as well (https://www.citusdata.com/product/cloud) built by the team that built Heroku Postgres. If curious on pricing you can find it at https://www.citusdata.com/pricing/
If you are looking for something that is more Postgres flavored (meaning we're just an extension to it so you get all the good stuff of Postgres such as JSONB, PostGIS, etc.) then we hope we'd be a good fit. And we run a managed service on top of AWS as well (https://www.citusdata.com/product/cloud) built by the team that built Heroku Postgres. If curious on pricing you can find it at https://www.citusdata.com/pricing/