The phrase "early reviewers" refers to people who get to experience or use something before it is available to the public, and then provide feedback or reviews based on their experiences. Full definition
A lot of early reviewers said that it «disappeared» into the experience of using the phone, but there I have to disagree. (androidcentral.com)
This is also a free way to find early reviewers for your book out of an interested pool of readers. (melanierockett.com)
With various carriers, service areas, and everything else that goes into cellular signals, I'm not surprised to see early reviewers having issues. (imore.com)