I stopped by Best Buy and picked one of these up. My location (Plano, TX) had the black/purple and white/blue. I picked up the white and blue. The cable was $20.99 (kind of an odd price) while the Dynex (Best Buy generic) was $19.99.
The cable works just as described. The "current" flows from the power source toward the iDevice. I tried it with both my iPad and iPhone 4, both were at different levels of charge. The speed of the lights does change with charge level. The lower the battery level, the faster the chase. When plugging your device in or unplugging it, it will take the lights a few minutes to react.
In the picture the cable looked to be a round, clear casing with the lights in the middle. The cable is actually flat, similar to speaker wire. The surface of the cable is split into thirds. White (or black) on the sides with the lights in the middle. The plug ends match the wire color, white or black.
One thing to note, the cable is just slightly shorter than the Apple cable.
To sum it up, since its the same price as other third party cables, it seems to be a good buy. If you happen to like cool gadgets, and since you are here you probably do, it's worth picking up. It's always nice to have an extra cable around. I will most likely take this one to work so I can enjoy it all day haha.