I have a TENS unit (The real branded TENS). I have bands specifically for my balls and metal rings for my cock. I've been thinking about getting a conductive butt plug, but I like my thrusting butt plug too much.
I have e-stim butt plugs that I use during role-play, typically when others are in charge of the remote control. The resulting hands-free orgasms can be amazing, it depends on the role-play and when and where we are playing.
I think my wife enjoyed torturing me with them more than I enjoyed the shocking torture. I hated it, but also loved every second of it.
Some of my most intense orgasms have been with my 2B, metal cockring electrodes and an electrode butt plug. Unfortunately, the 2B having problems right now. I need to get it seen to.