I think there is great potential for extending flight times with a collective pitch multirotor like this. Efficiency and endurance or range performance are not necessarily synonymous in multi rotors, as they have other constraints, like their energy source that restrict their performance. Likewise speed, endurance and range aren't the same set of constraints, and different solutions apply. The primary driving factor for hover efficiency in rotor aircraft is disk loading, with tip losses only a secondary concern, meaning having multiple disks/props is not necessarily much worse. Drivetrain losses are a separate issue, but are unlikely to be better in a collective quad drivetrain than in a heli. There's also other issues like prop strike energy and public safety etc, depending on the type and size of multicopter used, and where they are operated, that need to be considered.
However, most multi's are range and endurance limited by their battery energy density which need not be the case with these type of collective quads. Because the flight control is decoupled from the motors and RPM independant with a collective quad, it's much easier to make them fuel powered, which gives them a massive advantage in energy density, that despite the low fuel to power conversion efficiency of small combustion engines, still leaves it at a considerable advantage in comparison to battery powered mulit's.
Like this nitro modified version of nearly the identical collective quad frame:
Another advantage with a collective pitch quad is that control response is not as limited to rotor size and motor torque, meaning that larger props can be used on a quad and still have enough control authority. That in turn would result in a lower disk loading. Like with most fuel powered machines, vIbration and other factors like fuel handling and safety also need to be considered depending on the application if using a fuel powered quad.
Primarily, fuel powered quads would be good for long endurance in hover, but I think adding wings to an electric quad would be better for longer range like with a quadplane. Collective pitch control is also of high interest for hybrid vehicles, especially those with wings like tilt quadplanes and tailsitters etc, as they would allow propellor pitch optimisation for both hover and forward flight. Overall I find this addition very valuable as other types of aircraft and propulsion emerge.