Wonderful Rated 4 out of 5 stars
I had been using gContactSync for about a year when I happened upon Zindus in the Thunderbird "Get add-ons" window (Tools > Add-ons). Being only semi-satisfied with gContactSync I decided to give Zindus a try. Fast forward fifteen seconds (literally) and all my GMail contacts were synced perfectly (well, almost--see below) with Thunderbird, something I had almost given up on. I gave 4 stars, but really it is more like 4.5, and even then only because the Addresses did not sync from GMail.
The only issue I had was when trying to use "Sort Name By" to arrange my contacts by "First, Last" or "Last, First" (instead of Display Name). About a quarter of my contacts would then have no name. I looked into it and apparently these contacts had a display name but no first or last name. I only have about 150 contacts total, so I simply added a first and last name to the 40 or so without, and it's perfect. Thank you Zindus!