I don't look at air pressure, I look at the "arrow mark" on the shock and inflate till I see the top of the arrow. I do know that I need to pull forward a few feet and then back up a couple feet to get the shock to move before I "set" the pressure. I think the last time I set it, I was at around 95 psi before I saw the top of the arrow.
As far as roads go, when we left Goshen, we traveled down I-69 in Indiana to Kentucky. On the new portion of I-69, the road crossing most bridges was the worse I've ever been on. The dip and bounce going across bridges was terrible. Those points, no pin box in the world is going to reduce the amount of bounce and chucking we got. But for the most part, I believe the flex-air reduces the chucking and helps with the bouncing on "normal" bumpy roads. I can see the trailer bouncing in the mirror while we were relatively bounce free in the truck.
Does it remove all chucking? Nope, not even close. Does it reduce the chucking and give us a smoother ride? I believe it does. In my opinion it was worth the money. But my wife is not so sure. She thinks there is still too much bouncing for what we paid for the flex-air. I guess it's all a matter of prospective.