A Super Game Boy unit has been put up for auction on eBay and appears to be a prototype/demo unit. The label on the back is white and the serial code 0654 on it. There is also a Property of NMI sticker on the back showing that it was used for demo use. The person who posted it for sale also noted that it came with a NMI Super Nintendo demo console as part of a bundle from a former sales rep.
The user who posted the demo unit is silhouette_86 and has a feedback rating of 1765. The current asking price for the demo unit is $299.