This is a really handy device that helps prevent burns due to having far too high temperature on your hot water. It is a good investment to protect the skin from accidents due to unconscious bath-time oversights. Nobody is immune to forgetting to calibrate hot water. The device is a worthy investment bringing protection to address such scenario. Better safe than burned. http://bostonstandardplumbing.com/add-a-temperature-activated-flow-reducer-to-your-older-shower/
I think our "new" (starting our third year in it) house has that technology built in to the shower mixer valve. I like hot showers, but with this one, I can never get it to stay the right temp. It wants to keep me from adding HOT water, so my shower is almost always one of constant adjustment. It will get HOT, if you push the valve over all the way, almost too hot. But a nice use of technology, none the less.