If you get one, I recommend a well-built "therapeutic" one like the Bellicon. They are good exercise, easy on the knees and good for aerobic exercise and lymphatic drainage. That said, always check with your doctor first and if you have knee issues, then talk to a PT first to make sure you can use it and how to use it correctly. For example, if you have knee issues as a result of weak hip muscles, then you need to strengthen your hip muscles to help you have "solid" bounces. In that case, IF your physical therapist approved, then he/she would likely tell you to NOT use it to jump but rather to do very light jogging or mini "jumps" where your feet don't actually leave the mat of the rebounder. You can also get these with a safety bar that you can hold onto if you're concerned about falling. And lastly, I know that the Bellicon has the option of fold up legs so it's easy to store. That said, it is best if you leave it out b/c you're more likely to actually use the darned thing. No, I don't own the company but the rebounder was very, very helpful to me years ago when I was crawling out of a Chronic Fatigue Syndrome diagnosis. I later recommended it to many of my own patients.