Rated 5 out of 5 stars

Great addon until ver 55.5. All address books disappeared. Restored Thunderbird. Installed ver 55.6 with same nasty results. Again, restored Tbird. Last working version is 55.2.

Update: Restarting Tbird did the trick. Thanks for the quick response.

This review is for a previous version of the add-on (55.6). 

workaround here : https://gitlab.com/CardBook/CardBook/-/issues/1172#note_512218318

Rated 4 out of 5 stars

No user documentation. TB and Cardbook contacts don't agree. Not very usable in its' current (outdated contacts) state. Wish I could start from scratch and go from there.
And I don't care about any syncronization. Perhaps not use this add-on?
Update (after much investigating):
1. Deleted all address books in Cardbook.
2. Cardbook>hamburger>add new address book. And there it was: Import Thunderbird's standard address books.

Other than my initial mass confusion, Cardbook appears to be very usable.

This review is for a previous version of the add-on (54.9). 

documentation here : https://gitlab.com/CardBook/CardBook/-/wikis/Documentation