Mike, We have had STC's for most other Mooney models as a 3-blade and a 4-blade for the M20M but with different blade shape.
It is a fact of physics that HP is used/required to rotate mass (engine shops test run using metal clubs that absorb full HP yet make zero thrust). Reducing mass allows designers to used a more efficient/aggressive profile to absorb energy. This is what MT does.
Regarding 3 vs 4 blade cruise (drag) performance...At altitudes below approx 14K, given exact same plane with a 2, 3 and 4-blade prop, each with exactly the same blade leangth and profile; the 2 blade will be fastest by about 5 kts over the 4-blade. The 4-blade will have the highest amount of static/low speed thrust resulting in best take off and climb performance. Generally, as you fly into the teens with thinner air, the drag component is reduced. Now if you continue to make 300+ HP all the way, you have a massive advantage with flying high using the 4-blade prop. We have proven this with the Cirrus SR22 with TNIO-550 engines and this same prop.
Regarding flywheel effect...the Polar Moment of Inertia of this MT 4-blade prop is exacly the same as the 3-blade, wide chord Hartzell composite prop that is standard equipment on all new Cirrus SR22T aircraft. This same prop on those aircraft also added performance and reduced operating temps and has been a real hit with over 200 in operation with no problems. The dynamics of each prop/engine combination are required to be extensively ($$ expensive $$) tested by the FAA as part of the STC approval process.
The max RPM for this prop is 2700. Some models of M20 and some engine mod STC's reduce that. Our STC Flight Manual Supplement states "no change" to existing engine operations or limitations. So you continue to operate same as your previous prop.
Cruise speeds evaluated were done on the same plane, same day, same weight, same temps with full power and mixture set to full rich, then to best economy flows on a M20TN at 8K and 14K. The MT was faster by 3-4 Kts TAS in both cases.
The price of the MT 4-blade is about half of the cost of the Hartzell 3-blade composite prop used on the Cirrus SR20.
Thank you for the great questions...and for welcoming me to your forum. (This site is very easy to use and one of the best forums I monitor)
John