The phrase "review unit" refers to a product or device that is provided to someone for the purpose of them reviewing it and sharing their thoughts, opinions, and experiences with others. Full definition
This particular review unit comes with a silver and gold finish, and features a textured back that allows for better grip while also keeping away fingerprint marks. (androidauthority.com)
I recently got review units of both and look forward to testing them. (businessinsider.my)
The «update» mentioned below is only in reference to an update heading to review units for further testing / review. (androidauthority.com)