rotaflex is using the chain with the wheel mounted in the frame to tighten the cog. It lets you get away with not owning a chainwhip, but I personally think it's probably not the healthiest for your frame. If you get carried away, you could conceivably bend your stays towards the drive side or twist your frame into a pretzel.

pictures of the rotafix method:
http://204.73.203.34/fisso/eng/schpignone.htm