The remote builder works flawlessly on macOS; on other OSes, it may be enabled by passing --remote-only to the fly deploy.
Their support is amazing.
But
Their LHR region is the worst PaaS I ever used.
Starting from suspicious network latencies with GCP eu-west-2 region to advice from their support to redeploy until the VM is allocated on a server with enough free memory to accommodate RAM increase request 
, to service disruption when clients from EU were served times faster than from UK and LiveView was timing out for them, till suspicious RAM usage spikes and OOM crashes in the out-of-office hours on the internal tool.
They have the best DX out there, and flyctl is next to perfect, but using them is what actually makes me consider self-hosting.
Going back to the topic I want to mention, Ansible for DevOps [Leanpub PDF/iPad/Kindle] can help set up reusable and declarative deployment scripts.
