this is how you move the knot, you slide up UNDER it when going up, over it and down when coming down. I use the knot everyday in my job, it has never failed, i'm still here! use it when going up your steps or sticks, it works real well when hanging a stand.
If you slip going up or down your mainline it will suspend your weight without a problem.
It is easy to tie and untie( less than 20 seconds), and one harness with a 6' rope will do you as long as you have mainlines in every tree.
if you ascend using a harness with the linesman belt( like the gorilla ones that come with the stands), then you can climb, lean back, slide you hitch up, climb, slide, etc. you will NEVER fall when using that system.
hope this clarifies it a bit.
BD