I had Kelderman install front and rear airbags - they also recommended and installed a 4-link rear.
Not quite a year later, both upper bag supports bolted to the frame have cracked at the welds, one catastrophically, taking out the Rancho shock on that side. Kelderman's fixing, but with the same parts, not redesigned. I'm not seeing what will stop a second set of failures - maybe when it happens again I'll have the second leaf reinstalled and junk the Kelderman stuff. It's possible they're resellers of parts untested on Superduties, except in the field after a sale. Truck sees 90% highway miles; maybe twice a month on dirt roads, no outback.
When I received my truck from Kelderman, the rear was jacked w-a-y up high to clear the exhaust system. But to alleviate pinion gear shudder, Kelderman recommended deflating the bag down to a minimum height, yielding 1" of suspension travel on my 4x4 and a rattling, then damaged, exhaust pipe. I changed to an aftermarket pipe, my expense. To make it right I'll have to possibly lower the carrier bearing, reclock the diff., and lift the front to match, my expense.
After deflating the rear, my truck still looked wierd, rear stuck up in the air. So, Kelderman recommended pumping up the front bags to near max height, also yielding 1" suspension travel. The truck now has a stance reasonably near stock, but somewhat higher, with 1" travel front and rear in different directions.
There is an reduction in ride hardness, but don't look for anything but a pickup ride. The stock buckboard ride is softened significantly.
What's useful for me, and what makes me put up with major disadvantages in engineering and quality of installation (it broke big time less than 100 mi out of Kelderman's shop - they had to come up and fix), is the ability to load balance front to rear -and- side to side.
Short shot: I do not recommend a Kelderman front suspension. Rear suspension working, but with workarounds to major problems, thus far unsolved. Rear Kelderman suspension has load balance utility; noticable but not dramatic ride quality improvement.
Be forewarned: To adjust the rear bags, ya gotta get out and measure the height, then back to the cab to work the compressor or bleed air. Measure again. Back and forth both rear bags until it's right. Adjusting one bag with affect the height of the other. Takes time if you're loading/unloading during your day. You'd think a digital display of bag height could be implemented at the compressor/bleed controls.