I have the Dotan Sampson 25s. I don't like them at all. Maybe they would be alright if you sail in an area where you never hit bottom, because they only have 3 positions. Up, down, and stuck half-way inbetween. People who've sailed Prindles probably won't care about the stuck position as they're used to leaning off the back of the boat to shove the blade down anyhow.
They'd work great on little daysailor monohulls, but I don't think they are really up to par for catamarans.
The upper gudgeon has a tendency to break. I've gone through three of them. I hope I can find another because I've got a busted one at this moment. The resulting stress wreaked havok on my transom at the lower mount and left me with some fiberglassing to do.

Performance wise they work just fine, but when I get the spare change I'm putting a Hobie system on the back of my boat. My friend has a P18-2 and tried the Dotans. He now runs a salvaged system off a H-18 with good success.

So... if anyone still wants a set, we've got a couple with little use for sale.