You could probably find the 1-1/8” quill to threadless adapter without having to go to China. They are pretty common.

If the threadless steerer ID is the same as a threaded ID, then there would be no difference using it.

The flange nut looks like an interesting work around. I might be inclined to find something with a little bit better interface. A stainless spacer chamfered to fit against the angled reducer section.

John

Edit added: Using a compression plug instead of star nut is a smart idea since you loose access to the quill extender. It would be more of a pain to remove the star nut since you can’t tap it out the bottom of the steerer if you ever needed access.