Observations about Water Pressure Regulators.
Standard one sold in RV stores, brass or plastic cylinder, male hose thread on one end, female connector on other end... LOW FLOW device, basically JUNK, though it is a good pressure regulator the passages are way too small to pass even 1 gallon per minute.
HIGH-FLO, like the above but Camco has wings, others have a bright colored grip on the female end... Slight improvement but a long way from the prize. Still junk.
Sur-Flo, I give this one about a 9 when new, but as it ages it goes down till you rebuild it, at least it can be rebuilt
Valterra Adjustable - I do not have, many of my friends recommend but a few were not happy
Watts (And Zurin) (Plumbing store units) these are adjustable and some come with a gauge, some do not,, Mine are 3/4 inch (Both Watts and Zurin) since that was less expensive than a half inch.. I do not recommend the smaller ones (Smaller than 1/2 inch) My watts when new as fantastic, it is now nine years old and in need of a rebuild (The Sur-Flo is 8 and also needs a rebuild)
The Zurin is less than a year, It is set on 50 PSI and when you open the shower valves. that needle does not even wiggle.