Well, I've got an ET-312B, and a couple of the remote units Erostek made (the discontinued single channel one that was supposed to be programmable but they never released the software and the dual channel model).
Lots of attachments, and a bunch of users-written estim routines for the 312, as well as some audio files for feeding into the 312's audio input to get various effects.
I used to own a RIMBA TENS clone, so I'm familiar with what can and can't be done with those as well.
For the TENS type units, there are only a few adjustments, and most of them aren't things that the author of the tease should determine for the user. That pretty much leaves the "frequency" and the power setting.
One problem with TENS units is that the power controls aren't even *remotely* linear. Usually a range of 0 thru 8, and (for me) I didn't feel anythuing until 3 or 4, and the intensity went up sharply. from there. The increase in sensation between 7 and 8 was bigger than the whole range from 3-7. Think a steep parabolic curve or something, rather than the straight line something like the ET-312 has.
So that means a tease author would have to keep that in mind when telling you to turn it up. I usually went 3, 4, 5, 6, 6.5, 7, 7.25, 7.5, 7.75, 8. and those last 4 were still steep increases.
The frequency adjust feels like individual "blows" or "strokes" at the low end. Then at some point, it starts feeling like a vibrator. Then even farther along, the pulses are too fast for the nerves/muscles to react to and you get what's called "tetany". That's where things sort of just "lock up and quiver". It's *very* different. And you'll *definitely* know when you hit it. The sensation gets a *lot* more intense, even if you haven't changed any other settings.
The pulse width setting sort of makes things "sharper" the higher the pulse width goes. There's usually a 3 position switch that has N(ormal), B(urst), and M(odulate). Burst ignores several of the settings and isn;'t really that good for play purposes in my opinion.
Modulate is different from Normal in that the power is one for few seconds, then off for a few, repeating the cycle endlessly. This alternation tends to make the power on parts more intense by giving a rest and keeping the nerves from getting used to the stimulation and tuning it out.
The other "problem" with a TENS is that they have a designed in timer that shuts them off after 20 minutes. You have to turn the power on each channel down to "off" and then turn it back on. Which can ruin a tease.
Oh yeah, one other problem with TENS units. The stimulation power is based on the battery power. So with a fresh battery things are a lot stronger than one that's been used a while. Swapping in a fresh battery for a dead one can be a *painful* surprise.
Also, different batteries can be stronger. I found that the old Everready E2 Titanium batteries were a lot stronger than the normal alkalines.
Units like the ET-312 are stronger (oh boy is it stronger!) don't have the auto shutoff and have a lot more built in patterns. Better, they have audio input jacks, so you can use sound files on the computer to control the stimulation. This *does* pretty much require you to have one of the units to test things on yourself when you write a tease. Or have someone you trust to help you.
But with the non TENS built for play power boxes, you can just tell the user to set some kind of stim pattern and have them turn the power up or down. That will work in a regular tease.
You could do that in regular tease, an audio tease, or a video tease. With a Flash tease you could do that (with is pretty much what the estim section of Earn Your Orgasm does) or you can design for a unit that has an audio input.
I've got a copy of the now discontinued Desire Control program, and it let you do all sorts of things. One of the demos has you clicking on "cards" that flip over. Like in the Concentration game, if the two you click on match, you get a reward (a sound output that is supposed to feel good). If they don't, you get one that's supposed to hurt. And either way each match makes the good stim stronger and each failure to match makes the bad stim stronger. I think they get longer too.
Since the input on most of the units that have an audio in jack is stereo, you can have either spoken commands on one, and a set of electrodes on the other, or you can have two seperate pairs of electrodes, one on each channel.
With an audio, video or Flash tease and well chosen sound files, you can torture or tease. Mind you, quite often the stimulation that will eventually get you off feels "painful" because it's "too intense" (sort of like someone working on the head of your cock right after you cum) it's not *actually* painfuyl if you can force yourself to endure it, but your first impulse is to call it painful.
That's likely why a lot of folks can't get off from estim. But lower stim levels can probably get you off, but you may have to work with them (clench the muscles inside to help things along when the stim peaks, for example).
Torture is easier, and that's probably why Earn Your Orgasm takes that route. But you can get some incredible teasing too. There's one program on the ET-312 (I forget whether it's climb, or Combo) that builds up to a series of peak, with the peaks getting higher and the climbs getting faster. Then drops back and starts the sequence all over again. I want to cum *so* bad at each peak. But the stimulation drops off *just* short. And then when the sequence restarts... Oh Lord. But I can *usually* get there eventually. But I'm apt to be pleading or babbling long before I get there. Or worse, after an hour, it may be clear that I'm *not* gonna get there.
Back when I used to go to play parties with friends, I discovered that they could pretty much *ensure* that I'd not be able to get off by turning the power up sharply early on. Even if it was for less than a second. Being a masochist, the burst of pain wasn't something I objected to. But knowing that I wasn't going to get an orgasm was both not fun, and (to my submissive side) sort of acceptable. Though if I'm gonna be denied, I'd rather not know so early on., y'know. Still, fighting to get off even though I know it probably isn't going to happen makes for a good session too.
Smartstim.com has a lot of audio files and suggestions on ways to hook yourself up when using them. So folks could do a lot worse than raiding there for ideas.
And that brings us to the "final" variable. Where the attachments/electrodes, pads are placed. For getting off, I get the best results with an internal contact against the prostate (I use a PES prostate stimulator or a now unavailable biploar metal but plug where that inside part is one pole, and that's the part I use) or against my balls. The other contact is at the head of my cock (either a PES Sparkler around the shaft, and up against the under side of the glans, or a short metal penis plug)
Stretching the cock means the current has to flow thru more flesh, so it tries harder to follow the path of least resistance. In this case, that means the nerve bundle that runs along the top of your cock from the head to the base Iwith my old TENS on high power, I'd swear I could feel every *millimeter of that nerve path!).
If you are using the Sparkler or the like, you want the foreskin or shaft skin pulled back away from it. You want the current flowing thru the head, not the shaft skin.
Likewise, if the other contact is one of my balls it works best if the skin is stretched tightly across the ball and placed on the opposite side from the epidymus (where all the "tubes" connect. And as with the penis, binding things so the ball(s) are stretched as far as practical from your body helps make sure the current flows thru the ball, not the scrotum.
With my ET-312 I have their tri-phase cable, which combines the two channels into only three electrode connectors. One is common to both channels, the other two are still on A or B channels. They've got special programs that do amazing things with that setup.
But I like it with more normal programs. For most, I have the common on the cockhead. But for some it works better with the prostate as the common. Either way, I set it up with the three contracts being: cockhead, ball(s), and prostate.
On normal programs (including audio) that pretty much means that the common (glans or prostate) gets "double" the power/stimulation.
For torture, a pad on each ball can do nasty things. For that, you not only want the balls stretched away from the body, but also seperated as far as possible from each other (makes more current flow thru the balls and the spermatic cords). Don't tie them too tight as there are actually muscles in the cords and they *will* try to contract.
With a dual channel setup, you can also place a pad at each "end" of a ball, so the power lows along the length of the ball. This requires tricky binding.
Do *not* place a pad over the epidymus unless you are into *serious* pain.
Anyway, with the right stimulation program and moderate to high power, you will *swear* someone is crushing your balls every time the power switches on. That'd be a nicely evil thing to do to someone right after you have him edge.
But I'd really like to see what other folks can come up with.