Turns out Hi8 Air is well-suited for Win10 v1909. Clean install Win10, however, is a must. The much-needed disk space occupied by Android 5.1 (around 6G) also must be reclaimed. The final disk size is 29G, after installation plus some additional software, only 4-5G free space is left (also depending on how Win10 manages the Pagefile).
It is much easier to use a multi-port USB hub to link the bootable USB drive (with Win10 files downloaded from Microsoft), a mouse, and a keyboard. First, use Double Driver (freeware) to backup drivers before the clean-install process, then restore them after v1909 is installed, totally hassle-free.
Issues that maybe encountered include the following:
- To enter UEFI/BIOS, hitting ESC works, but not F7. Alternatively, go to settings, update & security, recovery, troubleshooting, and start UEFI there. Go to Boot page to change boot order, or to Save page to override boot order and hit USB to start installing from USB.
- After installation starts, an error window may show up, something about missing files, that eventually ends in cancellation. This is a USB drive issue, it may have to be slow-formatted in FAT32 first before downloading onto it the Win10 files. This step may have to be repeated a few times, very annoying. A brand new USB drive may also be OK. Eventually, installation will succeed leading up to a few Win10 setup pages. No activation is needed (even before WiFi is set up).
- Hi8 Air does not use SwitchNow, instead, it has Insyde Q25 hiding in the Recovery/OEM folder, this partition is deleted and replaced with a new 450MB Recovery when installing the new Win10. So, the 10-sec countdown Android-Wndows selection menu will still remain. To get rid of it, download SwitchNow from this forum, click it to see the boot into Android option, pick No, then pick Uninstall, now the tablet will boot into Windows directly. If Yes is clicked, the tablet will boot into the now non-existent Android and return with a Repair screen that requires hooking up both mouse and keyboard to reboot into Windows.