I have used an Oxygenics shower head in my RV for many years. It allows me to have a good shower using less water than the OEM shower head. It is especially good when dry camping and taking navy showers.
The change in temperature when turning the shower off and on is not really a function of the shower head, although most shower heads allow the water to trickle when it is turned off. This should prevent, or at least reduce the temperature change. For a real cure you could install one way valves in both the hot and cold water lines coming to the shower.
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