I have put down a deposit on one based on fairly extensive research and head-to-head feature comparisons between Autoprop, MaxProp and KiwiProp.
I also have a Gori two-blade folder on my old racer-cruiser and have sailed extensively on a full keel steel ketch similar to my new boat. The ketch has an 18-inch Autoprop H5 and now is able to achieve hull speed of 8.2 knots despite being underpowered with a 35 HP Volvo diesel. Basically, the prop and the engine are near-ideally suited. Plus, this heavy (36,000 lbs. disp.) motorsailer has gained appreciable speed in light airs, making her for the first time more "sailer than motorer", if you catch my drift.
The fore-aft swing of the Autoprop's blade disqualified it in my case, as I was unwilling to cut into my transom-mounted rudder's sternpost. The VariProp's blades extend no farther than the end of its hub when feathered, and that sold me, as did the ability to change pitch without hauling. Lastly, the design, unlike the Autoprop, will not feather in admittedly extreme conditions like "surfing under power" down a wave front. I spoke in person to the Canadian rep (a nice old German fellow who didn't look like he really needed the commissions to survive), and now the last step is to take the template down to the hauled boat and to see whether I can go to a 19" four-blade feathering from a 18" fixed three-blade fixed prop. I find that with a 14 ton steel cutter, you want a fair bit of stopping power and reverse thrust: the VariProp offers this, plus a more efficient way to match the power curve of my 52 HP diesel to the prop output. The extra speed under sail will be a bonus, of course, just as it was even with my Gori prop, where an already slippery boat accelerated noticeably faster in light airs and I had to rethink my sail changes vs. apparent wind speeds.
The usual cavils apply with any feathering prop, of course, but I feel that the benefits outweigh the negatives with the VariProp, even when the admittedly steep price is considered. I have been particularly impressed with the technical knowledge and the questions the rep has asked of me...he obviously knows his business and wants me not only to buy his product, but to buy the right one. Contact Jesco at http://www.nautilusvariprop.ca/
and ask for his list of endorsements, mostly local to the Great Lakes, but on a very wide variety of boats. The endorsements are unusual and I suspect quite legit because they list the things the Variprop isn't ideal at accomplishing as well as the large number of problems it solved.
Lastly, I will relate that when I told the Variprop rep that I intend to install an AquaDrive coupler/soft motor mount system to reduce vibration and transmission wear, he got quite enthusiastic and claimed that such a combination of universal joint coupler, welded in thrust bearing and VariProp was the ideal way to get the most out of his product and would bear benefits down the road when I avoided the sort of noise and transmission breakdowns that can afflict other passagemakers who keep the standard hard mounts and couplings.
I won't be able to attest directly to the performance of the Variprop until 2008, because I won't haul the engine for rebuild, weld in the bearing for the AquaDrive or pull the shaft until then, as I'll have to remove the rudder to do all this stuff at once. But my goal is to have a quieter, drier (I'm putting in a PSS) and certainly more efficient drive train in the run-up to our voyaging starting in '09.
Hope this helps.