Ross, like many others I've settled for a VT hitch with a micro pulley.
I attached a picture of my setup.
It's a 10.5 mm static rockclimbing line, 2.5 m long, which is long enough
for the relatively small trees we have here, but short enough to be out of my way.
The VT is 4-2 and made with a 8 mm line. I tied the ends together in a loop
just to make it neater, not necessary, double fishermans in each end will work
well.
I seldom prune pines and on removals I use a wire-core lanyard, so I really
can't say how this setup works with the sap.
If you still wanna go with a mechanical device I would recommend the
"Positioner" instead of the "Grillon" or "Gibbs".
The "Positioner" is made by arborists for arborists, is very smooth, clean and neat.
/ Oskar