I was eating my way through New York this past weekend and my hotel bathroom had a shower head with a built-in temperature display just like Delta Faucet's Temp2O. So now I know 109 degrees F is my perfect water temperature, and anything over 114 makes me say, "Uncle."
Presuming your shower's hot water flow remains constant during use (and I've stood under plenty that shift at random from lukewarm to burning my face off and back) the Temp2O removes all approximation from turning your fixtures and figuring when it's safe for your sensitive parts to step in. An LED digital display gives an exact water temperature reading during use. Three color indicators also light up to reflect cold, warm, and hot temperature ranges.
The shower head itself outputs 2 gallons per minute at 80 PSI, and includes settings full body spray, full spray with massage, massaging, shampoo rinsing, shampoo rinsing with massage, and soft drench.