A review of the system.
Generally looks ok. It has full Super GameBoy support.
One issue it has deals with the s-video/composite connection:
Got it, am not quite thrilled with it. S-video output doesn't work with the NES -- the picture is extremely grainy and fuzzy. In the YouTube video about the product, it's said this is how the hardware is supposed to be -- the NES wasn't designed for S-Video capability. I don't know if this is true or not. S-video works great on the SNES, but the original SNES had S-video capability anyway. I also can't make the SNES work well through the composite out -- it has a similar grainy and fuzzy look as the NES through S-video.
To make a long story short, it works decently as long as I run NES carts through composite and SNES ones through S-video. Kind of a pain.
BTW, search for retro duo in Google and then click on the Shopping link at the top. You'll find cheaper deals than what the guy on eBay is offering.