Most of what has been said above concurs with what I have found talking to owners who use Propspeed. It works by being 'slippery', but is quite soft, so the thing is to be careful about not running aground or into shallow water such that the prop is stirring up a lot of abrasive bottom.. If you can avoid that, then it appears good for the boat not used constantly, so Benn & Jeff B's & others similar comments are spot on I think. I'm going to try it next haul-out. Mind you, I was in real clear water the other day, (off Myora Benn), and had a good look at my (the boat's) bottom, and the Micron 66 is holding up well, and the prop and rudder weren't far behind, with just the usual hard anti-foul, and that was 2 yrs last Easter...
Any more news out there - trustworthy, that is - re this ultrasonic anti-fouling system. Now there's another, which is two electrodes, one each end of the hull, I gather.....?