I have Duogen and it worked very well in water
mode until the bearings seized up recently - mine is MK1 and later ones have better water seals
. Advantage is that, unlike the ones with a propellor on a cord, it doesn't drop down when you slow/stop and you haven't got the problem of a cord with a lot of twist in it to deal with. You do need to slow down to recover it from the water, as it has a horizontal vane to keep it at the right level in the water. I used it once in wind
mode but it's output in a force 7 (I was in harbour!) was disappointing. I haven't found the drag really noticeable and at 4 to 5kt it runs the fridge and instruments and charges the batteries a bit. Originally they said a regulator
might not be necesary but before I had one the voltage shot up to 16V when the fridge thermostat cut it out.