The problem I have with the Duo-R/RX is that because they are made with that light colored plastic, many of them have yellowed. Those that haven't.... well, they will sooner or later. It's not really a case of "if," just a matter of time. There are all kinds of "tricks" to clean up yellowed systems, but it's a lot of work, and in most cases they just get yellow again even quicker.
I have a black US Duo and it's the best looking console I own. A black Duo with the caps replaced (as mine is) is virtually indestructible. Sure, the lasers will go eventually (as with ALL CD-ROM based systems, including the Duo-R), but that's a simple replacement. Plus I never, ever have to worry about yellowing.
For the technically un-savvy, a black Duo is probably more of a gamble than it's worth.... But for those with any kind of technical ability, I'd recommend a black US Duo with a cap replacement any day. And speaking of the black Duos: the JP version looks extremely goofy with those purple buttons. US all the way.
All that said, an un-yellowed Duo-R is a nice looking machine. Nice score Apollo.