thanks guys for the good comments

More positive than I expected, I thought I was missing something fundamental

Yes I would use metal geared digitals. I was thinking about the arm fixed at the end of the surface, but understand the point of being in the centre to reduce surface flex.

The rads system I have heard has play, I cannot see how a direct servo to surface has more play than arm to pushrod to control horn normal set-up or the rads set-up

Any other views gratefully received

Ian