We got into this somewhat tangentially. Having found reports that suggest pelvic floor exercises for men can give erection improvements comparable to Viagra I was keen to see if Electro muscular stimulation might help. Many women report positive results from EMS for their pelvic floor so why not men? I have found that an anal electrode as one pole and a metal chastity cage as the other gives very strong muscle activity - way stronger than I can produce without EMS and the sensation, far from being painful, is rather like having a powerful low-frequency vibrator applied to your whole genital area. Although my primary aim is not gratification from the e-stim itself I can well understand how someone could cum from e-stim.
My wife has also been using the EMS with a vaginal probe to improve her PF and although we have only been using it for a few weeks the effects on both of us are significant with conventional sex much more sensitive than it has been for many years.