Experienced Flynn last year, we spent about 2 weeks making it work properly with our solution (We had a complex SaaS solution hosted on Heroku, with tons of addons).

We had some very bad bug that happened at the time (like deploying a new version made the dyno crash and we had to deploy a completly new environment).

Other than pretty bad bug, it was working properly, and did what they sell.

Good point is that the dev team is very responsive and we reported a bunch of bug that got fixed in no time. They also have a smooth updater when a new Flynn release came out, side bad note is at this time, it was kinda bugged (because of our specific setup).

For all those reasons, we choose to stick with Heroku at that time (we also tried Doku https://github.com/dokku/dokku, various AWS services such as BeanStalk, and DEIS http://deis.io/), but for sure it was the best candidate out there and I would love to give it a try again.