Good post UStick.
I might add that full sizes also use variable pitch for much the same reason that a car uses a gearbox:
To allow the engine to spin within its useful operating range, across the whole speed envelope of the car.

Electric motors has much broader and efficient operating range than any combustion engine, and hence is the benefits of variable pitch much reduced.

Ex. Lotus Elise, the "mother car" has a 5 speed gearbox and combustion engine, while the Tesla Roadster "daughter car" has a 2 speed gearbox and electric engine, and still outperform it in a straight line.

So the question is wether or not the extra complication, weight and "source of things that can go wrong" with a variable pitch propeller is worth it, when mated with an electric motor which has much less benefit from such a propeller.
I believe this project is complicated enough as is, and that keeping things simple (or as simple as possible) is important.