Good discussion. Now my 2cents. I have had quite a bit of experience with Master Airscrew props on trainers that beginners have brought to the field(s). In almost all cases where the student is considering getting a bigger engine changing to an APC prop will make the plane perform as if it has the bigger engine installed. With APC you will need to increase the diameter or pitch to keep the engine from over-revving. If you change from a 10-6 MA go to an APC 11-6 as an example. Many Sig LT-40's with OS-LA-40's will fly just fine with this combination. They barely get into the air with the MA prop. The APC props simply produce more thrust from an efficient design. This allows more prop to be turned. Try running the engine up. Change to the APC and try again. The extra amount of power will be quite evident.

Safety is always a concern however any prop will cut you if you contact it. Learn (or teach) safe modeling. Stay out of the prop arc and behind the aircraft when tuning the engine. Be aware of other pilots near by in the pits (they have their attention on their own planes!). Painting the tips white will make the prop visible. You can paint one only if you need to balance a bit. Removing the mold flashing (on all pros) will make them less likely to cut when starting as the trailing edges are quite sharp. Always use a "chicken" stick or other devise to start the engine (not your hands).

Common sence should always be used. I'ts like the wood shop saying: "DO NOT USE REMAINING FINGERS AS PUSH STICKS!"

EXCAP232