Great plugin, looked a high and low working through different plugins that do a similar thing but this is the simplest to explain how to use for a client.
However, one thing would be great that I can't find in any other plugin would be to have an alert or warning message on the Published post saying there is/are a draft version has been created. This will stop users making changes to the original which other drafts may be based on. In some cases, Person A would edit and update the live page if it were a simple change, simultaneously Person B may be working on a new draft based on an older revision without Person A's amendments.
Sorry if that sounds complicated, we're looking into maybe have a Editor's comments to let multiple users know that the specific page has a new draft but this can faulter based on human error.
Anyway thanks, keep up the good work.