I have done a lifetime of electronic soldering and have never seen anything like that. It looks very clever and useful. At first I wondered how the solder was being fed. Then I realized THUMB FEED. Wow!

You say un-fluxed solder, but I don't see why a flux core solder could not be used also. I think I have to build one or perhaps two or three of them. I may add a small spool so the solder does not run out so fast. And perhaps some kind of spring clamps so I can attach them and remove them as needed.

Great idea. As I said, I have a lot of experience with soldering and have never seen anything like it. You should get a patent. Really, before someone rips it off.