This is basically a full (not-OTA) update file for B20 version. It is really only good for downgrades to fix soft brick where your recovery is still accessible or to get OTAs. It will not help with bricks where phone won't boot past ZTE logo or into fastboot. It will also not help with stock mods since zip file is signed. And it cannot be flashed via EDL or DFU mode. I hope this is not the thing they were talking about when they posted that meme with brick wall and stock market recovery.
For fastboot restore, we would need new fastboot image, since i think there is a flash (or pull) limit on file size in the current one around 500MB or so IIRC
---------- Post added at 03:49 PM ---------- Previous post was at 03:41 PM ----------
Since this is a signed zip, there is no modifying it. Flashing modded rom would still require TWRP and could already be done since we have full /system dumps. And to use this to save you from bad flash, you will need to have access to recovery. TWRP could flash it i guess, but if you are in bootloader loop then not much help