How Safe is E-Stim?
E-Stim companies only generally sell units on the strict understanding that they are novelty items, but good advice would be to only purchase from a well known manufacturer with a good reputation and with a control unit that is CE marked. Beware of imported TENS units that are not designed for electroplay as well as using second hand and adapted equipment
Electroplay itself does have a couple of safety considerations, mainly to ensure that no current passes through the heart or across the chest, especially if pacemakers or other medical devices are in use. Based on this you should NOT use any form of Electro Stimulation if you have a heart condition, suffer from Epilepsy or are pregnant.
Contact points should be secure and if possibly lubricated, E-Stim could possibly cause burns at high levels with small contact areas.