What we need to consider is with an extremely small number of test units, the criteria they laid out should be strictly followed. @Sjef could certainly provide useful feedback for sure but has no review blogs with followers.
This closed beta is simply a pre full production launch; meaning that they likely feel close to be able to switch gears & ship. With that bring said reviewers are key due to their public exposure & skills evaluating headsets is a benefit.
Now if they were testing 50 to a 100 headsets then yes a broader range of testers would make sense. Plus if 10 is the target; I believe they mentioned having 8 so far.
After the closed testing is complete with hopefully the greenlight/thumbs up; we will be able to test & provide feedback ourselves once headsets start shipping.