I've got 350-odd users that I want to "convert" to guest authors.
I know that there is a "wp-cli subcommand" for 'create_guest_authors' but to be honest this is realm of science fiction for most of us. I got around this by copy/editing the 'create_guest_authors' function into my function.php and then running it in a sandbox template. Seemed to work OK. But...
It would have been far better if this feature was formally managed through the plugin under the DashBoard. May I suggest this as a feature for future versions.