He is speaking from the prop performance and efficiency perspective I think. I use some MAS props, but the better MAS choice is the Scimitar series. The K-series are noisy, less efficient, and are often under pitched. I prefer APC myself, as they are readily available, quieter and more efficient, and do not flex nearly as much. They are not as forgiving as an MAS K prop though.

I did do a test on 10x6 props testing how they loaded the engine (not a scientific test, but the results were interesting. APC and MAS K-series 10x6 props turned the same exact RPM on a K&B .28 diesel conversion. A wood 10x6 (I think it was a Zinger) turned more rpm, but the idle needed to be higher to be stable. Just FWIW. YMMV.