Alex--
I installed an MT prop on my M20J after my original prop sustained substantial rock damage 2+ years ago. The choice was to replace it with a similar 2-blade or to invest in the MT. I could not be happier with my choice.
The MT is eight pounds (+/-) lighter than the 2-blade, which I contend places less strain on the crank shaft bearing at the front of the engine. Probably not a huge amount, but certainly measurable. It is perfectly balanced when it comes from the factory. What is most apparent from the outset is that long cross countries are more enjoyable because of the lack of vibration and a decrease in the sound level; over 4-5 hours, the difference is really noticeable. There can be no harmonic vibration when running the prop because the core is wood and cannot support it. I have had no issues with the finish on the blades.
Almost simultaneously with the prop change,, I did an engine exchange, going from an IO-360A3B6D to an IO-360A3B6, and I do not see any difference in cruise speed. I consistently get 150K true now, the same as I did previously.