Myself and @nick when at Outlandish did comparative analysis of all the major container based PAAS offerings including Dokku and Flynn last year at around this time.
Building on the work done at GDS, we whittled down 18 plus offerings to three or four and built prototypes in them feel them out - Flynn was one of them but we decided against it in the end. After this and much debate we ended up using Red Hat’s OpenShift. It had the right combination of robustness, features, ease of use (simple but not too simple as to have no features so you’d have to invent a persistence layer) and backing by a major vendor that wasn’t going anywhere. It is built on existing technologies (Kubernetes) rather than reinventing the wheel and has a strong community around it. We then built a three machine cluster on AWS. I’ll let others closer to the project now fill in the gaps since then.
Perhaps @matt can share the big spreadsheet we did here. Should be in the COLA section of the GDrive. I think there is justifying documentation as to why we passed on the others as well. If memory serves there was one massive missing feature in Flynn (apart from not being based on something generic) which eliminated it for us.