not sure about the specifications of them, but i have installed two for friends which 1 has been black and the other white and the software for them is different... so I would assume that they have different manufacturers so they might be slightly different...
The lead is just a USB extension. it will enable you to move it around slightly to see if you can improve reception in areas of poor signal. An ordinary extension will do as well. The other advantage of course is that with a dongle stuck out the back or side of a laptop you might break it off inadvertantly. I nearly did that a few times with my dongle before I had a wireless laptop. I bought the black one from 3 without a lead and use it with a USB extension and it works fine