I own both. The Positioner is my personal favorite. The P. is more compact (it doesn't have a large 'handle' like the G.) and smaller overall than the G. With the P. it is easy to shorten your lanyard with the lanyard at various angles. The G. has a limited area in which it is easy to shorten the lanyard.
Both required (for me) some use before I found the right touch to lengthen the lanyard.
I also find that I need to have some type of rubber band on the P. Like the wire on the Microcender and Microjuster, the rubber band keeps just a little bit of tension on the lanyard so that the lanyard doesn't 'self-adjust' as you move through the tree. Other people say that the rubber band on their P. fell off long ago and they have not noticed a difference.
Since it is an option, I'll also mention that I prefer a snap, rather than a carabiner, on the working end of both lanyard systems.
Mahk