We used to call this Skaters Squat. Now I see it as a 1 leg version of Trap Bar DL so I'm constantly trying to get people to rename it. (Bad part is we now have 1 Leg Deadlift and 1 Leg Straight Leg Deadlift.)
His research shows that equates to a 2x's BW squat.
Mia is 16 and is using 40 lbs. Mark is 15 and is using 55 lbs.