I used a TENS from LG Medical Supply for exercise after my surgery. I was trying to regain continence and needed to exercise the muscles in that area. I set the TENS to force me to do a kegel contraction of my perineum once every 5 seconds. The unit I have is two channels (4 leads), and you can set voltage, frequency, duration and timing pattern of the pulses. It cost about $80–90. It is battery operated and has so much power I cannot get even close to using the highest settings.
I don’t know why any unit would be more expensive .As long as you have the ability to adjust the characteristics of the pulses a pulse is a pulse is a pulse.
I can’t tell if it worked or not. Did I get better because I used it or because I exercised by myself or because I just healed? Who knows.