Got this stuff as a "freebie" with another purchase. It's a bluish - green gel that you buff onto the data side of a CD. It does indeed come with a special black marker to mark the edge and inner circle of the CD with. I was most skeptical, but figured, what the hell? I applied it to a CD I know very well, as per the instructions, and even blackened the edge and inner ring with the special pen. Damned if I don't hear some kind of difference - it sounds better, but I can't quite place it. Darker background maybe, a little more presence maybe, something is different in the favourable direction. Anybody else try this stuff?