This is NOT an Add-On. It is a .blend file stuffed with node groups sorted in an asset library, so the easiest is just to download, unzip in a newly created folder and link that folder as an asset library. If you look at the first video in "Documentation" I go through step by step how it is done :).

Since I love doing patterns, I use this tool myself very much and that also means that I often find "good to have" stuff that I add, so it will be rather frequently but not on even intervals. I will also enhance and improve, but never change existing functionality of the old nodes. It should be just plug and play if you want to update later on.

No, it is not. You have patterns in there, but you should see it more like a very tiny version of Substance Designer. It will make the creation of new patterns much more smooth compared to just using the regular shader nodes in Blender. The best is often to combine the shader nodes that exists in Blender with the addition you get in my tool.