I have regulated guns that fall into three main types, with respect to the use of gauges:
- Two gauges, covering both the regulated pressure and reservoir pressure
- One gauge on just the reservoir pressure
- One gauge on just the regulated pressure
Of the three, I like the two gauge set up best - especially since those are both high shot count guns. I do look at both gauges, one to see how much air is left and the other to see if the reg is still stable, especially if it has set for long time - occasionally I have felt the need to blow off a shot a too before taking a shot I care about if I feel the reg has creeped up more than normal.
After that, if I can have only one gauge, I prefer it on the regulated pressure. I know how much I fill the gun with the fill devices gauge, so being able to see that gun is "ready to use" with enough air for at least a few shots is best, and I know that the reg is still stable. One the one gun with only a fill pressure gauge, I have no idea if the gun is still working properly without shooting a string over the chrony. That is my least desirable set up.
I will say that most of my regulators are Huma regulators, and since I have several I bought Huma's regulator tester. I find that it is a great tool to have, and I have great confidence in knowing what the regulator is set to before it goes back in a gun. That also lets me know how far off the regulated pressure gauge is, and I don't worry about it - I just read it to see if has changed.
