These Yanmars are called "auxiliary engines" for a reason. They are just for secondary auxiliary use whereas the primary function of our boats is to SAIL. Therefore, it seems to me it is more important that a prop produces the minimum drag when sailing than how efficient it is when motoring.
And I can tell a huge difference when I sail with my Max-Prop inadvertently un-feathered-- almost a knot's difference. To me that is huge. I would never go to a fixed prop. That's my $.02.
PSC31 #9 "Wayfarer"
The secret to sailing is good judgment. Good judgment comes from experience. Experience comes from bad judgment.