Malcolm,
I have a rudder on a Necky Louksha IV and while initially I liked it after paddling with it for about a year, I wouldn't get another. First, it turns your fixed foot rests into steering mechanisms and you lose the leverage of the foot rests while paddling. Second, when I am not using it and it sits atop the tail, I believe it picks up more wind and you feel the cross wind effect much more, thereby sooner or later requiring it to be put into the water.Except for extreme wind situations ( 10+ knots) I would rather use my body to turn the yak than the rudder.
I am only one opinion and many others obviously would disagree but I haven't found a rudder to be as pleasant as I initially thought. If you could find someone with a rudder, I would give it a try before you decide to put one on your new boat. You might like thembut I would give it a try first. FWIW!
Alex Warren