Now that the issue with the 'c' shortcut in the message composer window seems to be fixed (see https://github.com/opto/nostalgy-xpi/issues/29), I would give it a full 5-stars!
Just the fact that the settings menu is somehwat "hidden" at the bottom of the Tools/Extras menu (which is faded out in TB by default) makes it a bit awkward to find. It should be moved to the "Add-on Settings" menu.
Apart from that, kudos to the developer! I think you managed to migrate an add-on to TB78+ that is essential, if not the most essential productivity add-on at all for many power users.
curious bug. Options is not in the addons options menu, because no icon is registered for the extension...
Thanks to TB people for pointing that out - the code is ok, only the (unrelated) icon missing.
With due time, I will add that.