You can get either one or two support bars. If you need regular assistance while walking (such as a walker or cane), you should consider ordering a pair of support bars for stability.
If you have some trouble with balance with other activities such as walking or climbing stairs, having at least one support bar will help you.
If you think you may have trouble with balance but not sure if you need the help of the support bars you can always use the bellicon next to a wall when you first start using it.
Once your body gets used to the bouncing you will not need the support.