I followed your link to the Classic Editor plugin and have a few questions about.

My first question is this plugin ready to use on a live site? The description currently says:

Warning: This is beta software, do not run on production sites!

The second question is will the Gutenberg plugin need to be installed on the site before I can use this plugin? The description says that:
Requires WordPress 4.9-beta2 or newer and Gutenberg plugin 1.5 or newer

Any thoughts on this would be appreciated.