This might be of some interest for those who want to look deeper into the subject.
The July 26, 2001 posting by H-43 mentions the only problem that I have heard of; that of the systems linkages not knowing whether to apply CW or CCW yaw at low collective settings. I understand that this is applicable to Intermeshing and Coaxial.
http://www.unicopter.com/0742.html#Yaw
Relyon,
While admittedly an interesting concept it does use power, no matter how little that may be. It takes energy to move mass which to my knowledge can't be avoided.
True but the power is going into thrust.
Dave