Well I am off base about the mandatory sas for the 600, sorry!. .. .The 520 can swap ends if there is no sas, the 30 knot reagon is not the bad one, high speed is the problem. Chan Morse swaped ends in test, which lead to the sas requirement, if I remember his conversation correctly.. .. .If you look at all the critical parts, the Notar has a bunch more than a tail rotor. How many blades does that screaming fan have, and how many blade grips and bearings? The tail shafting is longer on a tail rotor, granted, with two or so bearing supports. I havn't seen a cutaway of the transmission to count the fan drive section, and compare it to a tail rotor gearbox. The tail rotating can has bearings and a control system, and is there a rudder? All that stuff is important and carries a parts count. In total, I'll bet there are twice the critical parts in a Notar.. .. .The one factor you all didn't challenge is the loss of payload. That small fan eats power, the tail thruster eats power. When we designed Comanche, we found that the power loss of the proposed, not built) Notar was its biggest detractor.. .. .The noise and protected tail are big advantages, so there is not one "right" answer, ever.. .Your collective enthusiasm says plenty, because you are the deciders, in the end!