First, I think that LuvToSail is confusing folding and feathering props. The Martec Elliptec is a folder for sure, and is pretty efficient going forward. As with all folders, static thrust in reverse is pretty poor. One design drawback in the Martec is that the blades are not geared together as many others are. This means that sometimes only one blade opens when forward is engaged, and severe vibration follows. This usually can be corrected by a momentary burst in reverse. Not a big deal, but can be awkward.
We had an Elliptec two blade on Insatiable One some years ago, and cruised thousands of miles with it. When it finally wore out to the point that no one wanted to rebuild
it again for us we went to a three blade feathering prop. Much more static thrust in both directions, but due to the flat blades inherent in these props their efficiency is poor, and we suffered a significant loss in fuel
economy (like 25%) which I wasn't keen on.
But, the increase in sailing performance is well worth the small difficulties in these props. You won't find too much change in ghosting conditions (where skin friction is the main source of drag) or in hull speed
conditions (where wave-making is eating all the power), but in that large inbetween range it really helps!
And don't worry about the prop spinning while sailing: simply putting the tranny in gear
briefly stops the prop, which promptly folds flat and can no longer generate any torque to spin the shaft.
So in this cruiser's opinion... go for it and enjoy!
Jim and Ann s/v Insatiable II lying Broken Bay NSW Oz