I imagine since it's the same as what I do, more or less, that's it's very effective. I've found that people are more honest when they're dreaming. They don't see a need to censor what they have to say.
I've never personally experienced anything like the attacks you describe. Well, maybe something sort of similar... One time I tried to get into someone's mind while they were drugged. I felt as disoriented and off-kilter as they did.
I'd be interested in taking a look at the machine, see how it works, and I'd love to try and join you. I'm definitely curious.