Rated 4 out of 5 stars

So far, the main difference between using this provider and Caldav is that subscription to multiple calendars is far easier with the provider (one step for all). For the rest, I cannot compare as the provider is temporarily broken (1.0.2). I rely on Philip for solving all this eventually! Thanks :)
By the way, those needing Caldav for multiple calendars should use this URL: https://apidata.googleusercontent.com/caldav/v2/calid/user , where calid should be replaced by the "calendar ID" of the calendar to be accessed. This can be found through the Google Calendar web interface as follows: in the pull-down menu next to the calendar name, select Calendar Settings. On the resulting page the calendar ID is shown in a section labelled Calendar Address. The calendar ID for a user's primary calendar is the same as that user's email address.

This review is for a previous version of the add-on (1.0.2).  This user has other reviews of this add-on.