Why do you need this app?
Mac OS X Address book does not sync with Google Contacts. It has basic syncing only if you have iPhone. Even with iPhone you need to sync the addressbook with iphone to have google contacts also synced. Multiple macs cannot be synced this way. This application solves the problem.
Syncing of other fields such as birthdays, is not supported on google contacts. This application uses a custom address field (which you can see on google contacts). Though this looks odd, it solves the purpose.