I've owned two of these units and purchased them from Bed Bath and Beyond.
On the first unit, one of the buttons broke. You could no longer dispense soap from that chamber, because the button was loose and wouldn't do anything.
I bought a second unit, thinking that maybe I was at fault for breaking the first unit. With this unit, the buttons work fine, but it doesn't hold the shampoo in one of the chambers. The shampoo is standard shampoo from Nioxin. It's not too thick and not too thin. My rather expensive shampoo would slowly drip our onto the tub, until the chamber was empty.
Maybe I need something more heavy duty, like the ugly ones in Lifetime Fitness. They may be ugly, but at least they work.