If the loads are kept in the perscribed % more closer to the light side I don't think the stress to the knee joint is much different than that of a depth jump? I have not seen research on this and have nothing to back it up but perhaps Mike can enlighten us?
I use these form of squats about 1-2 cycles a year. I keep the loads quite low (~50% max) and haven't had any problems with knee pain / injury due to these squats. The load is really not the point for this particular point of squat as what is on the bar isn't indicative of the force required by the athlete to overcome the bar. The force required by the athlete is dependent on the load and the speed at which the bar is allowed to travel downward (ideally a near free fall). Although I haven't done the calculations, when it free falls I suspect the load on the athlete would be somewhere in the neighborhood of 2.5-3.5x the load on the bar depending on the height of the athlete and the position the bar is caught at.
ELITETRACK Founder