What is the success rate of a sacral nerve stimulator?

Can you elaborate on the success rate of a sacral nerve stimulator? What percentage of patients experience positive outcomes, and how is this success rate measured? Are there any factors that can influence the success of the treatment, such as the severity of the condition or the patient's overall health? Additionally, what are the potential risks and side effects associated with the use of a sacral nerve stimulator, and how are they managed?