The Gaming Historian just released this video on this rather interesting add-on for the Famicom. I had never heard of this device before. Neat concept for its time. Check it out...
http://www.youtube.com/watch?v=r9PuSrn_H1c
Cracking video mate.
I was quite surprised to see this. Not something I would have had expected and it is rather interesting that games could be finished just a few days before release because of the medium being used!