It appears to be a burnisher that gets warm and causes the metallic medium to transfer from the foil. I got some of the foil yesterday to try and use on a landing gear strut but didn’t think to see if they had the pen. When I got home I started wondering how it would work on models.
I had never heard of it either. I found the foil at Hobby Lobby but didn’t look to see if the had the pen. May run out there today and see if they do. It would be pretty handy if it works.