I am not one of the testers. I use the file from this link:
The link provided by shadow is very slow, and so I used the one provided by shawonkibrea which is much faster to download: https://drive.google.com/open?id=0B1_tE5SkYZ6rcV93VkhkaEhiMjg
I think it should be the same file. Anyway after downloading, What I did is to rename the file to 2016070519113393599.zip so that it has the same name as the original file provided by shadow before doing the local update. I don't think this step is important, but just in case.
To share with you my experience, I have my battery charged to 100% before the update. Shadow's instruction said it takes 20 mins. My experience is about 21 minute at the robot updating animation, and another 7 minutes of booting at the Flash logo (yes, the Flash logo just kept animating for 7 minutes!). It looked like it is stuck but finally, the Welcome screen did came up. If you interrupt the logo animation, the update may not be complete and it may fail, so have to be patient. I think during this step, Flash should display a message saying "..updating.." so users will know not to interrupt it. I think a lot of people will think it got stuck and try to reboot, leading to a failed update.
If you try again, hope you succeed!