I just tried these for the first time today.
Kicked my a*&!!!
If you haven't tried them I suggest giving them a go. Really taxed the quads, hams , low back, CALFS, and grip. They also seem to force you to have great form by keeping you sitting back in your stance do to gripping the bar behind you.
Compared to deadlift, my hack sqaut was 60lbs less for a 1RM. I am sure this will go up the more I include them.
They are sure to be in my regular leg rotation now.