The article is wrong and Microsoft recommendation either. DVD/USB creation can fail, downloaded file will be deleted and you will have to download again (3GB+). The only reliable method is to create ISO file and save it locally (and save a copy on external drive).
The other things failed to mention: When upgrade fails or you are not happy from Windows 10, you might be not be able to revert to your normal workspace. You should do full imaging of your hard drive to the external media first. Then upgrade by opening ISO file then double clicking on SETUP.EXE. Skip entering keys during installation. Activate the upgrade on Microsoft server and then restore your original OS from the image file. Now you can upgrade your computer later at any time when Microsoft release stable release, not pre-beta like it is now.
Note for users who do not qualify for Windows 10 Pro. With Home version you will be not able to disable automatic updates. In such situation use DAZ on a fresh installation of Widows 7 Pro/Ultimate and upgrade from here.