My brother gave this a updater a try with a computer that never had Windows 10 and also confirms it works fine.
He had a desktop running Windows 10, but in order to upgrade the RAM he had to update the BIOS. During the firmware upgrade, Windows gave a BSOD, bricking the motherboard and apparently a common issue with his MSI motherboard, which can only be fixed with a replacement chip and SMD soldering. :doh:
So he dusted off a desktop that still had Windows 7 and gave the update tool a try instead of trying to apply years of Windows updates. About an hour and a half later, he was running Windows 10 and also checked that it was activated.