I think the Stable Loads are helpful. I made 3 changes out back on my 2013 F350 dually- Stable Loads, Air bags and the big fat Helwig sway bar. If I had to do only one thing it would be the sway bar. It doesn't help carrying the load but it sure helps on curves.
Don't get me wrong, I like them all and they all help in different ways. The air bags level the truck and are tuneable as I go down the road, the stable loads add some stiffness when loaded up, and the sway bar, combined with the others makes the truck handle pretty darn well on corners. If there is anything I really worry about it is overcooking a corner and flipping. I'm conservative enough to make that highly unlikely but still I have been surprised a few times by decreasing radius bends and I was real glad I added all my goodies to the truck.