Yeah, I have a Yeah. It is basically identical to a Dahon ya063 (found on the Chinese Dahon site), with a different name on the frame. In every other respect it is identical. The frame is identical to the one the Helios uses. It has all the technology that Dahon trumpets on their website (embed BB shell, visegrip, etc etc.
I replaced the back wheel with a quality one running 9 speed XT gear. It is a great ride.
What they do In China, the take the frames, load diferent componentry on them, and market that as a lower spec'ed model. Check out their site - they have a huge number of models, but they all use the basic Dahon frame range.
The Yeah bikes are made by dahon and are just rebadged.