I have a Zumo 340, one of the discounted ones Aldi were selling last year, and just use the mount that came in the box in the middle of the handlebars.
This puts the unit just below my field of vision which I prefer for an occasional check. I realise some may say this takes your eyes off the road but I think this is preferable to riding to the road on the satnav rather than what I can see ahead with my eyes.
This was brought home to me when working with a highly trained driver on a cross country route and their driving was crap. As an experiment I covered the satnav in the car and immediately their driving improved to what I would have expected from them.
Horses for courses but this is my experience and hope it helps the discussion here?