Does this product have one handle for volume (on/off) & one for temperature?A. Correct, The Kohler K-T10941-4 is a stacked trim. The bottom lever is your thermostatic control (temperature) and the top lever is the volume control (on/off and pressure).
Does this work with a shower head and separate hand shower to run both at same time and also separately ? In other words is it a diverter as well?A. The Kohler K-T10941-4 is not with a diverter. It only controls temperature and volume. It would need to be coupled with a transfer valve such as the Kohler K-T10944-4 to divert between outlets.
Does this control the volume of the water beyond off and on only?A.
The K-T10941-4 is a thermostatic set up, which allows you to set the temperature separate from the volume. The volume control will set the amount of water that comes out. The bottom controls temperature and top volume.