Here is a video showing the helicopter, the rotors are perfectly synchronized.
As there are not many such design helicopter, then my question are, is any aerodynamic weakness? What is its advantage/disadvantage of that helicopter?
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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.