I finally got time to analyze this add-on more deeper, but suddenly concluded the original screenshots provided in the very first post of this thread, are no more available as well as the domain. Be aware of installing something which is out of support.
I didn't check the add-on in action 'cause I have no time to download all those Google keys, but so far regarding this:
the code is used with all users (including logged in members) in topics and posts, when editing a message and when registering a new account
I could say it appears to be true. Following the miniBB architecture, this code will appear on each and every page where the posting form is available, and by default it's available on all the thread and internal forums pages. This is sort of painful. Also, it will appear disregarding if the account is being created or registered.