That's a fact Jack!
Control line models are the easiest test mules for trying to establish prop efficiencies -
The flight path is fixed and drag/speed is a constant and easily controlled path.
This allows one to get a very direct comparison on thrust developed on different props-or engines -or compare wing section drag -etc.,etc..
Call it a poor man's wind tunnel but I will take results done this way over any scaled down /extrapolated results from a billion dollar wind tunnel.
I am loath to use formulas which have never been tested in actual case scenarios.
On prop braking -- the exhaust system used on a given engine can assist in braking but most two strokers don't generate much braking force --a very flat pitch prop helps as it can rev like mad and still be resisting forward motion
Now -if you use an electric motor and back EMF ,you can really do some effective braking!
The new Hybrid cars do this extremely well- getting better fuel (gasoline) mileage around town than on the highway. The energy use is in a closed loop - still lots of waste heat but far better than the old gas buggies.