When using a 4-point-linkage, the linkages from the servos run in a straight line to the swashplate.
A 3-point-linkage does not permit this, here the linkages run diagonally.
The 120° servo mounting enables inclined installation of the servos, and the results are straight running linkages to the swashplate.
All Sky Fox based mechanics as well as on the Silence this kind of the servo mounting can be used.