It's finally out of beta and is now ready to rock 'n roll on a supported device. I was playing with the beta since release and it was solid. I just wrote the release version to a USB stick and tested it on my old ThinkPad that's running Linux Mint, until I find time to install Flex! For what that machine is used for, a full-fledged distro is overkill!
https://chromeunboxed.com/chrome-os-flex-out-of-beta
https://chromeunboxed.com/chrome-os-flex-out-of-beta