Maybe I'm missing something, but the prices look bad for what is offered. Why would you use them over say a managed server, for example from Hetzner [0] or Netcup [1]?

[0] https://www.hetzner.com/managed-server [1] https://www.netcup.eu/professional/managed-server/managed-pr...

I think Fortrabbit allows you to scale easily to have a fault tolerant infrastructure without needing know-how. Kind of Like Heroku in some regards.

A dedicated server is nice but if it fails and you have no redundancy, your service goes offline.