If I had seen the reviews before buying Windows from them, I would never have risked it.
BUT - I'm really glad I did.
I had no awkward questions about shoe size or passport number or anything.
After paying (with Paypal) I was given a link to a Microsoft site to download the package. OK - It was all in German, but the big button with "Installationsmedium erstellen" was obvious enough.
After downloading to a USB drive (which got formatted and turned into a boot device) I just started up the new PC, popped in the serial number they had emailed and off went the install. As soon as it was done, I confirmed the activation status with Microsoft (all OK) and went straight into the Windows 10 upgrade.
And that's working fine for me now.
I'm delighted with the service and (despite other reviews) wouldn't hesitate to use the company again.