From Aerodynamic view, what is the advantage/disadvantage of the Akagi Kaman K-Max Helicopter?
It's a twin rotor design, counter-rotating: no resulting torque on the airframe and no tail rotor needing to be powered. The twin rotors do not share a common shaft, with all of the extremely complicated control mechanisms that these require.

From J. Gordon Leishman, Principles of Helicopter Aerodynamics, section 2.15:


  The design advantage of a twin rotor is that all power can be devoted to providing useful vertical lift and performance. However, the two rotors and their wakes interact with one another, producing a somewhat more complicated flow field than is found with a single rotor, and this interacting flow incurs a loss of net rotor system aerodynamic efficiency.