retreating blade stall is less of any issue on compound helicopters if they include a wing. the wing can push that barrier back further, and even offload the rotor entirely of lift responsibility. even the stub wings on the Cobra and Apache provide a measurable amount of offload. not a whole lot, but some.
The nice thing about dual-prop compound helicopter is instead of using a tail rotor to coutneract torque, one of the propellers basically takes its place, providing the same counter force (one will provide more power than the other), at least until sufficient forward speed is achieved for the vertical stabilizer (if present) to be able to take over under sufficient trim (though this will increase induced drag). the down side of course is retreating blade stall, though is you have dual props, you probably have stubwings, or even a full wing, which as said, can offload the rotor. the downside of this design of course, is increased mechanical complexity (gearboxes and drive shafts to run the the rotation out the stubwings to the propellors and turn it 90deg, and of course the gearboxes on each side can't be identical either; one will essentially be a 270deg gear box)
so going coaxial then solves THAT problem, and allows the dual props to both run at the same speed/rpm, which will either simplify engineering, or reduce pilot workload/requirements, depending on how the design approaches the problem.
the simpler design is coaxial + 1 prop. reduced mechanical complexity in that there's only one drive shaft to the single prop, which if located in the rear is a known design method because thats how "normal" helos do it anyway, yet even then its reduced complexity as theres no gear boxes required to turn the rotation 90degree, and no 45deg gearbox to run a short drive shaft up a vertical stabilizer (as in the Cobra/Huey).
but of course, coaxial rotors bring their own added mechanical complexities as well.