The softwaregeeks link is completely legit, I’ve bought 3-4 Win10 licenses from them. You get a key sent to you, download the Win10 install from Microsoft and enter the key when prompted.
It’s an OEM license which is the only difference with respect to the retail copies at £200+, the only real difference is you might have to do an automated phonecall to reactivate the license if you change the motherboard of your PC.
Also, with respect to Win10 tracking concerns..
https://www.oo-software.com/en/shutup10
Been using that since Win10 launched and it allows you to completely control what Win10 does with respect to tracking and reporting back to Microsoft, just have to re-run it after a major update (I usually rerun it after patch Tuesday every month).