Probably enough has been said, but I will only add that I have the "TrailAir" (which is now owned by Lippert, but I got mine from the original owner, Dale--met him at Goshen, IN)
Have used it on two different fifth-wheels. The in-truck hitch is probably somewhat better, but the advantage of the pin-box "TrailAir", or similar, is that it goes with the trailer, not the truck. I was able to transfer from one trailer to another by purchasing some basic parts.
I think it is worth having. Yes, I do have to air-up about every week when on the road, but I carry a small 12 volt air compressor just for this purpose.
I've traveled nearly 100,000 miles across the US and into Canada with this pin-box air cushion and would recommend it.