There is no upgrade version. The full version can either be clean installed or it can be used to do an upgrade.
Clean Install Windows 10 - TenForumsTutorials
Repair Install [aka In-Place Upgrade] - TenForumsTutorials
The benefits of upgrading are
1 He will probably not have to reinstall his applications.
2 He will probably not lose any of his own files during an upgrade.
3 By upgrading, the existing Windows 7/8 licence is automatically detected.
On the other hand, before starting such a major task he ought to back up all his own files anyway, check that he has the installation files & product keys for all his applications & check that he has the product key for his existing Windows.
Clean installs are reputedly less prone to faults caused by gremlins that have been left behind from the old OS.
So he could consider
1 Upgrading for now, then
2 Clean installing when he has enough time spare.
That $105 'OEM' copy might be okay [MS sell theirs for $139].
The only significant difference is that there is/was a short entitlement to MS support if you buy from them. If that is of interest you'd have to look into it yourself because it's not something I bother staying up-to-date about.
But the help in this forum is better than MS anyway.
There is no decent method for identifying pirate copies of software in advance so it is not possible to judge whether or not that $105 version is legitiimate or not.
Denis