I've been using these inserts for years because I have knee issues.  They actually work as well for me as my custom-made orthodics, and because they are RELATIVELY inexpensive, I can have multiple pairs so I don't have to shift them among my many shoes.  I started wearing them because I had arthritis in my knee, and as long as I wore them my knee didn't hurt afterward because of the way I was walking and distributing my weight. Eventually my arthritis worsened, and I had total knee replacement surgery, but I still think it is important to walk properly.