The coaxial counter-rotating blades eliminate the need for a tail rotor but the main stack is mechanically complex. I have a small fleet of indoor RC helicopters with coaxial rotors. Cheap and fun to fly!
The “Design Considerations” section outlines the strengths and weaknesses of the design.
https://en.wikipedia.org/wiki/Coaxial_rotors
One of the proposals for the Army Future Vertical Lift contract is this one from Sikorsky:
https://en.wikipedia.org/wiki/Sikorsky-Boeing_SB-1_Defiant
It’s a pusher prop heli with contra-rotating blades.