I am on my first long trip in the trailer after installing the Oxgenics shower head. As soon as I am camped in one place for two weeks running I'll know for myself.
My friend John is visiting, photographing Death Valley with me. I read him some of the posts in this thread and he said the following:
John: Tell them I, a Ph.D. mathematician, said that the Oxgenics shower head probably produces a more forceful stream, making people use it for shorter periods of time, thus saving water.
But I think he's right-- the water stream from the Oxgenics seems stronger than the stock shower head, so I probably use it less. I'll know for sure in a few weeks.
p.s.: John is a good guy-- he has an Escape 21, after all.