This looks really great. Here's the installation guide that they make you put in an email to get to: https://support.google.com/chromeosflex/answer/11552529
You can use the Chromebook recovery tool (a browser extension) to write an installer image to a flash drive. I'm pretty sure you need 8GB of space or more. Others have intercepted and extracted the downloaded image, but I never cared enough to use that approach.
This process doesn't work with all Chromium derived browsers, though, probably because they added extra permissions to the extension because I wouldn't normally want a browser extension to have raw disk access.
https://chrome.google.com/webstore/detail/chromebook-recover...