While not related to the "female perspective", I concur with your (really excellent) description of what you get from a TENS unit. Or, don't get, if you know what I mean 😉
I've been exploring with an inexpensive TENS unit I purchased quite cheaply on wish.com (direct sourcing from China, much like Alibaba). It's got 2 independent channels and about 15 modes -- but they're all based on parts of the body. And not the fun ones, either! It's got knee, back, neck, shoulder, arm. leg, etc. -- and none of them really provide the right stimulation.
It's also got a few more descriptive ones: Knead, Scraping, Tapping. I try those, and they can feel nice, but mostly kind of...boring?
On the positive side, it has plenty of juice -- I rarely get above 50% before it becomes too painful.
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I was hoping I could prove to myself that I'd enjoy e-stim with a cheap TENS unit before having to commit to a much more expensive purpose-driven unit like from Erostek or E-Stim. Alas, I'm afraid I'll either have to risk the cash or just accept that perhaps it's not for me?
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For what it's worth, if you're still interested in trying TENS units, this one is currently < $30 at Amazon: https://amzn.to/2KaiP3n.
Good luck, and happy exploring!
-g