Rated 5 out of 5 stars

For me, zindus is better than Google Contacts for one BIG reason - it doesn't lose any changes.

How I tested it:
1. take Thunderbird offline (status bar bottom left)
2. modify contact(s)
3. go online

Result:
* zindus: changes are preserved and sync with Google
* Google Contacts: changes are silently lost!

I go on the road so for me, syncing changes made while offline is a must.

Feature-wise I read on zindus.com that addressbook google group and picture sync is coming and I'm happy to wait.

This review is for a previous version of the add-on (0.8.13).