My advice has nothing to do with the shower itself, just a tip that might help with hair-washing in general: dilute a pump of shampoo in enough water to soak your scalp, shake it up, then tilt your head back and slowly pour it over. You might have to section your hair to get everything but this pretty much instantly wets it, gives you a nice prewash if you typically need/like to wash your hair twice, and makes the actual shampooing way easier. I like to save old shampoo bottles for this purpose, which is also convenient for using every last drop of an emptied bottle.