Multiblade props are not as effecienct as single blade props. CL racers use a single blade prop with a mass balance for a good reason.

The more blades you have, the more prop drag, wich means less power transfered into thrust. Additionally, more blades mean the following blade is closer to the wake left by the leading blade, reducing the effeciencey of the blade. In general, you will always be better off with a two bladed prop vs a three blade with respect to effeciencey.

3 bladed props are used in RC for three reason I can think of off the top of my head: sound reduction, increased braking, ground clearance. Lower tip speed with a 3-blade reduced sound. The extra drag and more dense prop arc increase braking. Smaller diameters increase ground clearance.

3 bladed props also put less stress on engine bearings due to gyroscopic forces, but that is mainly a non-issue for RC, i.e. it is very hard to break a crank in flight with RC engines.

I don't know what's up with the 3-bladed trainer. My guess is they selected a 3 bladed prop for three reasons: increased ground clearance, controlable (i.e.reduced) performance and it looks differnet setting thier trainer apartf from the zillion other RTFs.

Cheers