...I would like to leave it in place virtually all the time but would like to understand more about the likely windage effect. (if I need to drop it when going upwind then it seems a bit pointless)
I don't think it's pointless. It's easier to furl the foresail and then drop the well behaved "tube", than to drop a spinnaker.
Afterwards, you may tie the "tube" to the net and leave it there, ready to hoist (or take out the halyard only). Or stow neatly furled in the cabin.
The spinnaker requires more work to set again, unless you bag it rigged. But then the cabin entry will be obstructed and there will be at least three loose lines on deck to worry about.