I'm not sure I understand the question being asked here, but I feel the need to contradict Diosoth for a second. You can purchase a brand new Retro Duo off the Amazon site for around $40 shipped. Amazon.com sells them for $45 w/ free shipping. I'm not sure where $50 plus shipping is coming from. I'd imagine Ebay would be cheaper than Amazon, as that is usually the case, but I haven't checked.

If you're asking whether it's worth it to purchase one of these, I wouldn't. You own a couple NES and SNES. If you bust the tabs inside an SNES you can play most import Sufami games. (All the ones you'd be able to play with the Retro Duo anyway.) Not sure, but I'm going to assume this plays Famicom carts too. Well I'd suggest getting an actual Famicom. They aren't incredibly expensive and they're a much better collector's item. IF that's too expensive AND you own a top-loader, then a simple converter would be a great idea. I've gotten some knockoff converters pretty cheap, but they don't work so well if your NES is a toaster that you need to line the carts up perfectly inside to get em to work (if you see wht I mean). I consider all these unlicensed clone systems to be shoddy, having owned several in the past (tho not this particular one). Most manufacturers use cheap parts to keep the costs down. Sure it's cheap compared to buying two of the actual consoles (or four depending on how you look at this thing), but that's the big problem. It's that cheap because the parts used are cheap. Most clones feel like they'll break in your hands.

So I'd say only get this if you want to start collecting clone systems, but not b/c you either think you can get rid of the real systems for this (unless you really aren't a collector and don't care about playing all the games, seeing the colors & hearing the sounds as they were meant to be produced, and don't mind replacing this thing in six months when it stops working) or because it seems like a better option for getting into import games. I certainly wouldn't spend more than $40 for a new one, and definitely much less for a used one (they are $30 on Amazon for used).