Rated 5 out of 5 stars

by Martin Rosenbach on Jan. 8, 2017 ·

I am quite happy that this app 2-way syncs my android phone with TB via CardDAV service provided by my Synology NAS (DSM 6.0).

On android I use "ContactSync" - the price (1,50 EUR) is a good deal (made donation for CB as well!).
Even categrories can be seen on the phone!

Main pitfalls:
Synos CardDAV service can deal only with vCard Version 3.0 - this is not documented.
While transforming my existing contacts my android phone exported its local contacts as vCard Version 2.1 - CardBook did not complain but imported nothing. Had to convert to vCard Version 3.0 before.
"vCard Grid" (java program) did the job (but needs all keywords in uppercase!).
When activating CB, TB became very slow in the GUI. Eventually found this article: http://rainbow.chard.org/2013/02/19/thunderbird-high-cpu/
Did not observe the CPU-storm described there, but applying the proposed modification made the GUI working as smoothly as it was without CB! (you may try a more moderate change, say only 10 times).

This review is for a previous version of the add-on (15.7).