At the top of the mizzen it is out of the way and has better wind exposure, but this position has several major disadvantages:
The longer cable run means much
thicker wires, resulting in significant additional weight, not to mention the weight of the heavy unit even higher up in the rig.
Worst of all it is extremely difficult to service
at the masthead. Can you imagine sitting in a bosun's chair at the top of the mizzen trying to repair of remove this heavy, unwieldy thing that is trying to spin in the wind, a few feet above your head.
When my unit failed, mounted just above the spreader, I was able to stand on the spreaders and easily reach the equipment
for testing, and then attach a halyard
while I was removing it, and lowering it down to the deck
To me, it was still quite a difficult job that would have been almost impossible above the masthead.
Mounting halfway down the mast is a bit of a hazard for the mizzen staysail, but there are ways to take care of this.
I have a spare halyard
that I move over to gently jam the windvane
(after activating the stop switch) before hoising the mizzen staysail. This works like a charm, and I have had no problems using the staysail for the past several years.
I highly recommend the mid-mizzen position.