I've had an ntsc Retro Duo v2 for a couple of years now, and I've had no problems with it. The video output is not as good as the real thing, but it plays all of my SFC, SNES and NES games. I recently picked up a 60-72 pin convertor and some FC games, but haven't had a chance to try them out.
The controllers are okay, but of course not as good as Nintendo's, and the NES port in my unit is extremely tight.
Overall, it's great considering it's a clone.