I am buying them all! I have found step to not hurt my knees as much as some hi lo stuff. I blew half my ACL once not sure when, but my doctor was shocked that I "didn't notice". I think I did as a teenager playing volleyball.
I do have to modify some of the jumps, I don't jump as high, and I have to use a 6 inch step, higher than that, and my knees get SORE for days, perhaps weeks.