I have them, and with my PUP, which has just under 500 lb tongue weight, almost 4000 lb GVWR, and no WDH (weight distributing hitch). I put 30 PSI in the bags. There's no magic number...just level the TV by trial and error. I basically return the ride height to the same position as when there is nothing on the hitch and nothing in the bed.
Measure from the ground to a convenient point, say the bottom of the hitch or some other spot and replicate that with the air bags when fully loaded.
I'm also loaded with 28 gallons of fresh water, a generator, fuel, a canoe, firewood, two 60 quart coolers, a propane fire pit, 2 spare propane tanks, a couple of dogs, a
fully-loaded aluminum bed tool box (ideal "trunk" on a pickup), and so on. Yet, 30 PSI does it.
You don't say what you're towing or what you're towing with, but 50 PSI is a lot. First time I towed my PUP home from the dealer, I put 50 PSI in the bags, and the rig looked like a humpbacked whale (high at the hitch) and rode like a Flintstone car.
Note that with a WDH, you may need considerably less pressure in the bags, because the WDH will "lift" the rear of the TV and move some weight to the front axle of the TV.
You may wish to add some air if you get some porpoising when going through whoop-de-doos on the road. Even with a WDH, you may experience some wallowing, and firming up the rear spring rate with the bags might help. 30 PSI might be too much in this case. My RAM is pretty soft riding, and even with a much smaller PUP, the back end wallowed, and the nose pointed to the sky (blinding oncoming drivers at night). The air bags solve that completely, and the handling is far more secure fully loaded.
For what it's worth, they warned me to never run the bags empty. Always keep 5 to 10 PSI in them to keep them from losing their shape and distorting...and possibly being damaged.
With no WDH, I also increase the tire pressure in the rear tires on my TV. Just driving around empty, they call for 35 PSI. When towing, I raise the rears to 40 - 45 PSI. I'm running 275/60/20's, so they run a bit softer than a typical truck tire.
I love the air bags! They are also wonderful for a trip home from the home improvement center with 1500 pounds of concrete and so on.