I made an extensive prototype with it and definitely do not recommend it. It's really just a UI clone of the Medium editor. It doesn't work at all the same way

I made an extensive prototype with it and definitely do not recommend it. It's really just a UI clone of the Medium editor. It doesn't work at all the same way under the hood and instead tries to use ContentEditable as the store of a document. Any approach which works that way is doomed to failure. ContentEditable works fine as an input but you need to have a pure mapping from all inputs to an internal structure which only your editor controls.