Rated 4 out of 5 stars

Excellent AddOn and must have for Nextcloud, Zentyal and SOgo.
Could be five stars but looses color in calenders in the windows version on Zentyal's SoGo - all calendars are grey (color choosen in Linux is kept with Nextcloud).
Update: Unfortunately one can not change the color of Zentyal SOGo. If you connect the calendar natively using lightning you can overwrite the color from TB side.

This review is for a previous version of the add-on (0.7.18). 

Due to popular request, the selected color in lightning will be transmitted to the server.