Hi Dartanjan,
Version 2.9.0.7 only has a message for admins in a small box at the top on admin pages only, everybody else will not see this. There is no easy way of removing it and to be honest, I don't want people removing it as it serves as a reminder about the state of the theme. Current list of issues is here: https://github.com/gjb2048/moodle-theme_essential/issues - current list of known bugs affecting the M2.9 version is here: https://github.com/gjb2048/moodle-theme_essential/milestones/Moodle%202.9%20version.
Cheers,
Gareth