I have a couple of those little brass pieces of Junk if you want one...
now the serious point of this post... I have use a WATTS 3/4 inch (more on why that ZURIN (also 3/4) when hooked up (not often) But for totally different reasons I've gone to filling my on board and using the water pump.
ONe park I stay at logged 120 PSI
THe watts new held a nice steady 50 PSI LIkewise the ZURIN I'm told the Valterra Adjustable does well (Way less expensive)
As the Watts and Zurin age they start to restrict flow (Pressure drops under load) but they can be rebuilt cheaply and easily.
WHy 3/4.. well they were cheaper than the 1/2's and of course easier to adapt to garden hoses.