Adam,
Reducing the RPM of the rotor will require that the pitch of the blades be increased to maintain the same thrust. This is an advantage in that the efficiency (power/thrust) is increased.
Unfortunately, this also increases the risk that a perturbation, malfunction, etc. will cause the rotor to loose all lift.
The Boeing Hummingbird is an Unmanned Aerial Vehicle therefore its crash would be unfortunate but not tragic. The loss of life in a helicopter crash is much more serious. With all regards for the relatives and associates of the deceased, helicopter fatalities have also resulted in the demise of a number of aspiring helicopter manufacturers.
IMHO, and subject to elaboration or correction by others.
Dave