Tens Units .. Pean relief and Fetish tool.. What is the difference?

Hi all of you,

What is the difference between Tens Units (Transcutaneous Electrical Nerve Stimulation Units) used for pain treatment and that used as Fetish like (Fetish Fantasy Series Shock therapy – bdsm kit) or (Nexus iStim – electro stimulator)?





note: Sorry for the spelling mitake in the title: here is the correct one:
Tens Units .. Pain relief and Fetish tool.. What is the difference?