Advantage of using Spanning Sync vice Address Book to sync contacts?

[Rhet]

I'm currently using Spanning Sync to sync several calendars but my
contacts are synced via Mobile Me which is about to go belly up the
end of June. My Macs aren't compatible with Lion hence iCloud is of
no use to me. To keep my Macs' contacts in sync, I plan to use Google
Contacts instead of Mobile Me. Is there any advantage to using
Spanning Sync over Snow Leopard's Address Book to Google sync
feature? I tested the Address Book Google sync and found it wasn't
syncing birthdays. Does Spanning Sync sync the birthday field to
Google Contacts correctly?
Cheers,
Rhet