that thing looks so fucked, I like the regular hack squats.
it's really easy to use though.
you adjust the shoulder pads, you place your feet, and you push. it is just the feeling of being "up" there.
but this one is awesome for the back. you don't feel it really much. I do it once in a while, but still I prefer regular squats. some times on a smith machine, sometimes alone.
we also have air pressured machines. there's one for standing squat. never tried it though.