And chatting with some people both on here and on reddit, I took the leap and bought two tens units. A basic box one (Tens3000 S), and a remote controlled one (Tens Omega Wireless). I've now done a number of scenes involving electro and wanted to share what I've learned.
It can be torture (yay
). At higher levels, having one of these things on is painful. I don't know what I expected electric shocks to feel like but it wasn't this.For safety, I've only ever placed the electrodes below my waits, usually on my thigh, once on my foot. I've never tried them on my dick. I've used them at max power but it fucking hurts, my bf only keeps me there for a second or two before turning it down. We've done a pretty involved torture scene that lasted over two hours, but I was never being shocked continuously for more than 15-20 mins (more on that later). The only effects I've had after a scene have been a sore muscle (probably a combination of it tensing up and me struggling). A caveat - I am youngish (late 20s), have no heart problems, and probably moderately healthy/active, so safety considerations may be different based on your own health & heart situation. Additionally while I often tie myself up and sometimes even initialize the electro torture on myself, I only ever do it when my bf is around and can help (or hurt) me.
In more involved scenes, where my bf is actively playing with me, he'd turn the power up all the way for a few seconds then cut it off. The effect is a short incredibly painful moment, and he'd elicited a few gagged screams this way. We've had more luck with the tens3000 unit for this. It simple and intuitive enough that my bf can simply crank the dial when he wants to shock me, and turn it down when he wants me to get some relief. The remote controlled one has been trickier, it often turns off or doesn't respond when he tries to zap me. Unfortunately this has meant my fantasy of him sitting at his desk doing work and zapping me every once in a while while I'm tied up on the couch hasn't really happened.
Instead for less involved scenes where I tie myself up and wait around until he wants to release me, I've turned the remote unit on from a bound or cuffed hand, set it to the setting where the intensity grows and shrinks, then thrown the remote control out of reach. The effect of this is I'm constantly in slight (varying) pain and quickly transition from being peacefully tied to wanting to break free. It's a fun game where past me wanted to tie me up so good I can't get out without my bf, and present me desperately wants to break free. If I do get out, I shut off the unit re-restrain myself, and try again. Eventually past me wins and present me is stuck enduring bondage and electro torture i can't escape.
I've noticed with the remote unit there's some sort of internal timer failsafe. I haven't explicitly timed it but it feels like after 15-30 minutes it automatically cuts off. This is a nice safety feature, though in recent scenes when my bf has left me restrained way longer than I'd expected, I've ended up running out the clock on electro torture and then having a good hour of laying around tied up without any stimulation. In some ways this is a nice relaxing reprieve, other times this is a fun teasing scene in itself (especially if my bf tickles/edges/does some quickly breath play whenever he passes me on the way to the bathroom/kitchen) sometimes it's just boring/anticlimactic.
Eventually my bf releases me. Sometimes we'll do a fuller scene before he lets me go, other times not. I never know what to expect.
I've really enjoyed dabbling in electro. While there's definitely more I'd like to try for now it's a very fun, easy torture to set up during a bondage scene.
Thanks for sharing your experience and health/safety insights.
Love to be tied-up, gagged and tickled ! 
