Hello Kaartman, as Cory Kendall and the article says that this tutorial is for Windows 10. However, if you are using Windows 10 and still not getting the TestHooks in your Registry editor, do follow this.
1. Open your Registry editor and navigate through the path, what is mentioned in the article.
As the TestHooks folder is not there, you need to create the whole thing.
2. Right click on the LogonUI folder (Which is in your left hand side), then click on New and Key respectively.
3. Name it TestHooks.
4. Click on TestHooks folder, right click on the empty space on your right hand side, select New, create a new DWORD (32-bit) Value.
5. Name it Threshold.
6. By default, the Value data should be zero(0). That is what you need to have.
It will help you to get Windows 8 like logon screen. However, if you want Windows 10 logon screen, you need to change the Value Data. If you enter one(1) your logon screen will be changed.

That is because this registry tweak is for Win 10 Insider Preview