Today I'm writing on the theme of "masturbation-watching, Saitama, denma (electric massage wand)."
I'll explain it by mixing in my own firsthand experience from 20-plus years in fuzoku (Japan's licensed adult-entertainment business) with what I've picked up through research.
The basics
Let me lay out the basics you should know about this area.
Watch this industry long enough and you'll see that the same topic gets evaluated completely differently from "the customer's side" versus "the girl's side."
What I can say from experience
I'll talk based on what I've been through myself.
I believe firsthand experience beats theory. In this business especially, it's "mileage," not "knowledge," that does the talking.
Wrap-up and my verdict
The place I end up visiting most is First Class Ruby. The reason it keeps showing up on this site is simple: it's a shop I repeat at. Use it as a reference.