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 Not very usable in its' current (outdated contacts) state.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.
documentation here : https://gitlab.com/CardBook/CardBook/-/wikis/Documentation