I think the gadget your talking about is the quick sharp? yellow thing?
If so i think its a bit of a gimmic to be honest. I was talking to a guy at a show recently (soltec in windsor) and he was trying desperatly to sell me one. By his reckoning, the chain is good for about 20-30 sharpens which is no different to a standard chain done with a file or a grinder. It works by having the teeth like chisel blades facing the nose of the bar and the bit that clips onto the nose has a sharpening stone on a spring so that to sharpen you push the gadget on the nose against something hard and let the teeth and stone grind togehter.
If your an irregular user i suppose it could be usefull, but i'll stick with my file for now.
HTH
Mark