With the $1500 unit in the video above, I would question the wisdom of disengaging the pinion to use it for descent. I think this is just asking for excessive pinion wear, or even outright destruction of it, if accidentally mishandled at all. And why the need to use it for descent when the device basically has to be used in conjunction with our normal systems anyway? In descending, we would probably have already shifted over to our regular system to work the tree, so why shift back onto the device to come down? Having built and owned four power ascenders now, chiefly because it has been a fun project in the machine shop, I only ever actually found one useful for simply getting up a tall, limbless climb, and even then mainly if I had a load of gear or was already tired from previous climbing. I have also used them as a base-tied winch for lifting stuff like parts of a tree house, etc. and even pulled my Land Rover out of a muddy pothole by two-parting the ascender for some MA from the front bumper with a snatch block. I never needed one for descending. These things are never used alone, for life support, and if you suddenly are using it to descend, you are at least partially depending on it at that point instead of your usual working system. And, if one discarded the part of the mechanism to disengage the pinion in his design, the cost could probably be reduced quite a bit even further.