I love my US Duo, but man it gave me some shit over the years. I bought it new from Turbo Zone Direct in summer of 2000. I didn't really start playing it all that much until 2007. I already had to recap the sound area at that time, got it region and S-video (with a CXA2075) modded, then replace the lens in 2008 due to bad CD-R use. I started playing my Duo a lot more around 2009 and the sound started going out again by 2012. I sent it off to thesteve on the PCEngineFX forums and got the entire system recapped, a few tweaks, and he took out the old S-video mod thanks to his new and improved S-video mod that is much simpler.
Here is the funny thing about RGB vs the new S-video mod for these systems. You actually get a more overall accurate and stable picture with the S-video. He does a cap ground to the video out, and adds a stronger cap on the board in front of the HuCard slot to get rid of the noticeable jailbars and mild RF like wavy interference. Also, the color palette is more accurate like what the composite video outputs. RGB of course will have a sharper picture and completely eliminate the small amount of shimmering and dot crawl of the S-video mod (which is very minimal BTW), but you still have the jailbars and inaccurate colors. Depends on preference I guess, but I am happy with the newer S-video mod and have no need for the RGB mod really.
With that all being said, either get a Duo-R or a standard Duo that has been completely overhauled if you really want the design. Another thing you might want to know is that the Everdrive doesn't like region modded consoles and games can load up glitchy. I got lucky with my US Duo due to it being a better region mod with very short wires. Sometimes I have to reload a ROM like Soldier Blade, and some others.