Hetzner gives you bare (or virtual) metal that you have to install stuff on, and maintain it. Fly.io and similar give you a higher abstraction layer where you

Hetzner gives you bare (or virtual) metal that you have to install stuff on, and maintain it. Fly.io and similar give you a higher abstraction layer where you throw a Docker container and the stuff below and around it is managed for you. Basic suff like OS patches, but also autoscaling, load balancing, request routing, etc. Does the 4x difference make it up? It will depend entirely on you and how good you are with the things fly.io abstract for you, and how much you value your time spent on it.