hi there Martin
I am a big fan of windvanes and put one on our maramu last year
on my old boat (30ft) we had a monitor
this time we chose a hydrovane as we used on on a family boat before and they are really good
The monitor will require lines lead to the wheel - which i'm sure will work but will need some thought
i mainly went for the hydrovane as it does not drive the main rudder. you lock the main rudder off and the hydrovane takes over - so acts as a completely separate and spare rudder system which was a big draw for us on long haul journeys as a back up
we routed the hydrovane pole through our swim step and that worked well. We also bought the longer shaft version so the whole vane part was positioned just level with our solar arch.
The monitor rudder swings side to side as it steers - so i'm sure youve been thinking about how that might work with your swim platform
We have stopped using the electric autopilot for all but motoring (which we avoid if at all possible)
it was such a relief to get rid of the noise of the electric autopilot and its inherent complexity
The SM have a wonderful redundant autopilot system so i can totally understand that for SMs a Windvane might be overkill but once you have sailed across an ocean with a windvane silently helming for weeks on end its hard to entertain anything else - wonderful inventions.
Good luck fitting yours - i'd be interested to hear how that goes