Building such a thing is not that a high effort, reliability, extensibility and scalability are the things which are not easy to implement. For a small scale like hobby projects it definitely makes sense to use such stuff but not for things where you want to press a button to provision new nodes in different regions with e.g. GKE Autopilot or Render.com. Like things where you rely on a bulletproof CDN e.g. from Vercel or Netfliy.
btw. I'm curious why their installer is 73MB in size: https://get.coollabs.io/coolify-installer