Furi OS was what turned me away. Never heard of it and that makes me realise we don't have an android alternative OS which is permanent. Do we have any OS which is permanent? Shouldn't we have one?
FuriOS is a derivate of Droidian, which in turn is basically Debian with Halium support. So it's pretty much Debian + some custom patches for usability, hardware support, performance, so on. We intend to upstream as many of our changes as possible as time permits, but right now we are laser focused on improving the experience day in and day out.
Once you turn on full disk encryption, the phone will reboot once and begin to encrypt the entire filesystem in the background. Further reboots will require that you input your FDE password (which can be different from your lock screen password/PIN) in a minimal rootfs-based UI.