This is the guts needed for a lot of Deltas tub and shower trim kits.  What makes this particular unit stand out is the flow control.  Very few shower faucets offer this.  I do not having to pass through the cold before you get to the hot found on most valves.  This unit can be set at the proper temperature and then turn on the flow.  The temperature setting can be left where you like it and just the water started and stopped.  This is also a great way to save water and energy as only the amount of water needed is sent to the shower head.