I have continued using Cobook and have no interest in "Full Contact" as it does things that are not relevant to my needs and it does not do everything that Cobook does, all of which is relevant to me.
However, today for some reason I find that I am unable to connect my Google account to Cobook so I have gone looking for alternatives.
The only one I have found so far is "Cardhop", which is similar to Cobook but not as good. It is quite expensive but you can have a free 21 day trial: https://flexibits.com/cardhop
Lots of specialist cloud-based storage systems seem to be closing down so I am hoping that "Full Contact" does the same and that the people behind it come to their senses and pick up support for Cobook again.
In my opinion Cobook is/was staggeringly well designed, bug free, perfectly functional and the best contacts manager for Mac by a very long chalk - especially if, like me, you want to integrate contacts already stored in different places, eg. iCloud, Mac, Google Contacts, Facebook, etc. AND want the convenience of a Menu Bar widget that is instantly accessible whatever else you happen to have open at the time.
Cardhop is a poor substitute but the only one that I have found so far.
Liz