Reviewed version: 1.4
My score is 1 star. It is clear what this extension should do. But that is also where the documentation ends. There is no installation/configuration instruction.
My score is 3 stars. Very interesting functionality. At least for my own install of CiviCrM because I can sync my contacts in CiviCrM with my smartphone :-) If it is great functionality towards greater organizations and NGO I am not sure about that yet.
Code QA ****
My score is 4 stars. The code is very good! The code looks like the rest of the code of CiviCrM so CiviCrM developers can maintain the code quite easy.
Ease of use *
My score is 1 star. I could not test this section because you need a Google Apps for Business or Education account. I have only a free google apps account. So I could not figure out where to set the OAuth key etc...
This extension is interessting but as I didn't get this extension to work I cannot give an overall review.