You'll feel the forces trying to deflect the movement of the nose from the straight path you're wanting it to go. An exageration of this is the spinning bicycle wheel or the rotor on helicopters. When the wheel or blades are rotating, it is quite hard to rotate the frame or center out of plane with the rotating disk without getting unwanted results.
Absolutely correct! I assemble my own bike wheels - both mountain and road - and when you spin a lightweight road bike wheel it is MUCH easeir to change the plane of rotation than when doing the same thing with a heavier mountain bike wheel.
At the kind of rpm's we're talking about with gas engines, having a prop that weighs less than half as much as these 120-gram APC's has got to be a good thing.