Rated 5 out of 5 stars

Well Done
Very well done ;)

I sync to 5 different computers over 3 US States + a mobile laptop, and the fact that my calendar can be manipulated and adjusted as need my several different people, without having to sign into Google, is excellent.

I eagerly await the fix of the bug that will not allow off line reading or archiving, but this small issue has not been a deterrent for over 2 years now.
The bug is also outside of this addons purview.

Thanks for your hard work and the latest update

Regards
SGT. E. V. McKay

This review is for a previous version of the add-on (0.5.2). 

Hello SGT McKay

Thank you, I'm glad the provider is helping your business! Unfortunately, providing offline support is not as easy as it sounds. This is an issue that should be fixed in the core product instead, anything else would be quite a hack. We need to find a performant way to generally synchronize two calendars, which may be hard especially with many items in the calendar. We (the Mozilla Calendar Team) have already added readonly offline support, but there are some server-side issues with the provider w.r.t recurring series. If you want to try this, enable the experimental cache in the calendar options and restart.

Hope it helps!