I attended a lecture on placebo not too long ago in fact. It was on a friday evening which shows my dedication.
It is as Dali writes. The company who makes I-Doser do what they can in order plant expectancy in their customers so there's an element of manipulation to this. The required training is also perfect for training a placebo response. Of course there might be a real physiological effect that is caused by the bi-naural beats, but either way you get a placebo effect on top of that and your experience comes from either placebo or the placebo and the actual effect of I-Doser put together. The point is; either way it's there - whether it's all or just part of it.
Something I didn't think of before is that it could have a meditative effect as well. By relaxing and focusing ones thoughts on something, people slip into other levels of consciousness. This is often accompanied by feelings of relaxation, clearness of mind, feeling heavy or almost like your body is not there, comfort, waves of tingly feelings and so on. You also get better at meditation with training which is consistent with I-Doser and how it should be used. A rough way to put oneself in a meditative state may for example be to close ones eyes and count backwards from 100.
If you close your eyes and focus on a sound, that might have a similar effect so then the I-Doser experience could be caused by at least three things; placebo, meditation and binaural beats.