Only if it's actually generating more thrust. It could also be generating less thrust. The problem is many people never go so far as to measure the thrust or speed. They put the prop on, get more RPMs and conclude that it's more efficient and therefore better. Then since they've already convinced themselves that the prop is better, they perceive that it's also better in the air, perhaps partly from hearing that the engine is turning faster. I accept that some people actually measure and conclude a particular prop works better for their plane/engine combination, but many just go by what they hear from others or conclude from the engine turning higher RPMs.

So in other words the shape of the prop is not a factor in performance/efficiency, but the right prop/plane/engine combo is what ultimately gives you performance/efficiency. And conclusion of performance/efficiency is all achieved by trial and error or are there tools for this (like a tach for RPM)?

Yes & no. The shape of a prop definately has an impact on its performance, but without a chunk of knowledge & prior experience (if then), you can't usually tell if a particular shape is correct for your particular engine/airframe/end-use combination. This is further complicated by the fact that the construction material is also vitally important in making a decision -- & the wrong material, regardless of blade shape can make a mess of the selection. There is a place for each of wood, reinforced nylon & reinforced epoxy somewhere in the spectrum of modelling applications.

Experience & ongoing test-trials are needed to get close, while appearance counts for just about zero in the performance game. For example, APC makes a range of scimitar-shaped props with significant variations in root-transition shape, blade offset & effective aspect ratio. They also make a somewhat similar, but less scimitar-like series of props with very slender tips. They all look somewhat similar, but also have clear visual differences. Without prior experience, or reference info from APC, you just can't tell which one (if any) will be right (or even close) for your application. They all will work, but not all will work particularly well.

The same thing holds for MAS, who also make both scimitar & conventionally shaped props -- and just to confuse things -- they also use two different kinds of synthetic construction material.

Looking at a prop and saying to yourself -- "that thing won't work, the tips are too skinny (or too wide)", is quite likely to be very wrong. Even experienced modellers will make mistakes in pre-judging prop performance.

Similarly, making sweeping pronouncements that APC, or MAS are superior to each other, is complete nonsense.

Getting back to reality, there are some rules of thumb that can be helpfull.

1) Don't get emotionally attached to a particular brand, and don't get a hate on for one either.

2) Size props for the correct engine load, so that the engine rpm falls between the torque & power peaks (if you don't have torque info, size the prop for somewhere between the advertised power peak rpm & ~2,000 rpm less)

3) In terms of engine load for mid-size 2-blade props (40 - 90 size engines), 1" of diameter is roughly equivalent to 2" of pitch. (eg. 10-6 = 11-4)

4) Select props for the correct end-use application. For example, with training aircraft peak performance is a secondary consideration to toughness & low price -- reinforced nylon is a good material to use here, regardless of who makes the prop. Don't use wooden props for seaplanes (instant destruction upon exposure to water spray)

5) Select props for the correct airframe application. For example, in training applications speed is an enemy, therefore larger diameter & lower pitch props are a better choice than smaller dia, steeper pitch props -- choose acceleration/deceleration & climb rather than speed.

6) If your model has a large blunt cowl, it is advantageous to choose a large dia prop & sacrifice pitch to keep the engine load in the right ballpark

7) Slim-nosed models can use small diameter, steep-pitched props, but will lose acceleration & climb performance in order to gain a little speed.

8) Under-propping costs flight performance and wears engines more quickly (rear crank-bearings on 2-stroke BB engines & valve-train parts on 4-stroke engines).

9) Over propping costs flight performance (particularly with 2-strokes), wears engines more quickly & raises combustion temps

10) Suck-it-and see