I can't decide if I like it or not. It's great for my wife; her shoulders are too narrow for the conventional hack squat machine, it hurts her. This she can do no problem. I used to like to use the conventional machine 'backwards' sometimes, it got my hamstrings pretty good that way, and used normally gave me a great pump in my quads. This thing, I feel it mostly in my hamstrings. I'll have to fool with foot position and see what I can do changing it up that way.
One thing about it: I always have to be very careful with conventional hacks not to hurt my knees. The right foot position (usually pretty far out in front) generally takes care of that. This thing doesn't seem to strain my knees at all. Wonder if that's why it was developed.......