The tank's minimal docs say they're pre set at 40 psi from the factory. I think I'd leave it alone.
That's a normal way to deliver them, but doesn't imply they shouldn't be adjusted. 40 - 60 PSI is a very common well pressure switch setting, and it's easier for a plumber to relieve a few PSI during installation, after checking with a gauge, than to haul a compressor or pump down to the basement to charge the thing. And if you're one still running 30 - 50 PSI, also easy enough to let 12 psi out thru the valve.
This doesn't apply to the OP, if he's running a constant-pressure rig, but for everyone else, this is important:
Having your tank bladder over-charged can result in both short cycling AND massive pressure losses before cut-in. Round numbers for demonstration, let's say you have a 40 - 60 PSI well pump switch and a tank bladder pre-charged to 50 PSI. Turn on the system, and the well will charge everything up to 60 PSI cut-out, before turning off. Then you use some water, and get nice linear pressure down to 50 PSI, at which point pressure in your plumbing almost immediately plummets toward zero, as the bladder is completely expanded and there's no water left to push out of the expansion tank. If you're taking a shower, you'll notice great pressure, then a total loss of water, then it comes rushing back with a bang. Not good.
Having your tank bladder under-charged doesn't cause this problem, hence the recommendation to run 3 psi below cut-in. However, going too low also reduces useable tank volume, what they call the "draw-down" capacity, between pump re-starts. This is because there is less air space remaining in the tank, when the bladder is under-charged. So, even though there's water left in the tank, there's no bladder left to push that volume.
Setting the bladder right at cut-in would maximize the draw-down capacity, but run the risk of pressure loss right at cut-in. Hence the advice to pre-charge to 3 psi below cut-in.
For OP: I've never rigged a constant-pressure pump, they weren't a thing back when my family owned a plumbing business. But I would strongly suspect that one would want to set the bladder pressure (empty tank) right at your constant pressure setting, or just a few PSI below it, for the same reasons: maximizing draw-down while preventing pressure cycling.
