I did Low Max yesterday and had a great workout. It's not at all hard on the knees, but you do have to be aware because there is a lot of pivoting on the floor and some of it is fast. The moves are familiar but cued quickly - I previewed because I'm a sloooow learner with choreography and I got most of it with one or two brief rewinds. I go between a 4" and 6" step with Cathe cardio to protect my lower back, but I did this one at 6". The workout is not a space hog either - you'll need room to walk around your step plus a little room off either end - you do a grapevine off the side of the step - but you can easily modify to accommodate a smaller workout space. LOTS of leg work in the blast sections - your quads, hamstrings and glutes will be on fire. And a VERY thorough stretch at the end.
I'm looking forward to doing this one again.