This was suggested for strengthing knees and ankles on another website. I have no idea how beneficail or detremental it could be, maybe Bill will comment on it.
I have never used one, but once I have recovered I plan on adding it to my routine.
I am rehabbing a broken ankle as you know. I am just working on getting flexibility back in the ankle right now, but hopefully I will start working on strengthen it soon. If you like I can post the exercises that the physical therapist has me do to strengthen it once we start that phase, but be warned these exercises will be prescribed based on my particular problem and may not be of any benefit to you.