Vince-
I haven't used them yet, but I've seen them and know a few folks that have used them. The theory os that it takes the torque away from the knee. The knee does not have to twist against itself when in pretty much a sitting position, knees spread, and toes pointed back in. The stirrups fit the ergonomics of that position and are easier on the knees.
on a trail ride or riding into camp, etc., I often have to take my feet out of my stirrups to ease the discomfort of my knees.
