It happened twice so far, yesterday and today.
By "shaking" (fast/very fast) the helix back and forth (not in and out) I can feel it touching my prostate and a nice feeling but no build up. Then, if I continue, (I guess it depends on the rhythm & the angle) a sensation builds up. That sensation is (nearly) the same you get when you are jerking off/fucking but more intense as it begins to feel real good (you know you will soon cum). I can really feel the prostate and my penis slowly getting hard as it is building up. Once I am fully hard it's nearly instant ejaculation and it is very powerful making moan & shaking. The duration of the orgasm is longer too.
I never heard it was possible to cum with only prostate stimulation. I was expecting a super-O, although the sensation is very different than what I get with no hand prostate stimulation so I knew it wasn't. It's like if my body turned a switch "penis" and any prostate stimulation is like stimulating my penis.
Is it possible to still have a super-O like this? Why is it making me ejaculate?
You can ogram and cum from prostate stimulation alone. I had this happen the first time my wife fingered me. Instant orgasm and ejacuation. You're creating a lot more pressure on your prostate with this method than the hand-free approach and therefore, it's going to cause you to cum. And, once you do that, the refractory period sets in. Party over. At least for 30-minutes or so (assuming you're a younger dude). For us older guys, it may be even more time.
Now, there's nothing wrong with this approach IF your goal is to orgam and cum. See, you're already accomplishing that very well. But, if your goal is to ORGASM WITHOUT cumming, you're going to have to take a different, more measured approach.
The Aneros is designed to be used with no-hands. This much more subdued than what you're doing now. You have to be patient and pay attention to more subtle sensious clue your body gives you...a tickling sensation deep inside, behind your pelvic bone...a throbbing in your anus...little jolts of something that feels like electricity running down your thighs and arms, up to the top of your head...rubbing your nipples and feeling like someone is rubbing their finger on the inside of your penis. This takes patience and time. It is not a "pile-driver, push to orgasm and ejaculation" experience.
I don't think you'll get a full-body, continuous Super O this way. I think you'll have great, super T orgasms. But, as long as you go down this route, the Super O will elude you.
It's like a cat, dude. You have to learn to let it come to you instead of trying to chase it down.
Separate yourself from your penis, Grasshopper. And heed newguy8762's erudite advice.