After operating it for over 4 years I am sold on it.  Its reverse seems as powerful as its forward force.  Solid power in fwd or rev from a dead stop or at slow speeds.  In motoring or motorsailing it provides good, fast propulsion and during sailing very little drag.  Easy prop removal and bomb proof attachment to the shaft--see brochure.  Seems well matched to the Amel with good cruising speeds from 1600-2700, quite a bit of our cruising motoring is up and down from 2000  It will let you go above 3200 with no problem--can't remember how high it goes.  It seems to like motor sailing as well when there is lower load for a given rpm.  Works well with our shaft brakes. The German based company will immediately respond to emails or phone calls.  http://www.spw-gmbh.de/en/features-of-the-variprop.html   also  http://www.spw-gmbh.de/en/variprop-2-3-and-4-blade.html