These fittings are becoming a common product even in new construction. !!! I'll post pictures later on but I've seen new construction where they are being used for connections entering the home that transition poly pipe to copper, along with main shutoff valves at water heaters.
My concern at the water heater would be the heating of the O-rings over time, causing them to leak. That literally is all that keeps them from leaking, and the connections via spider clips keep the connection together...even though they can spin almost like a loose socket when installed.
At Home Depot they sell a braided flexible connection that allows for a compression 3/4" to a water heater dielectric nipple to 3/4" copper, cpvc or pex with a sharkbite crimped right into the end of the braided hose.
