I installed Kings on my F150 about 3 weeks ago. They are not battled tested yet (other than blasting over speed bumps). As mentioned above, on the road, the ride is noticeably improved. It is firm and much better controlled, but by no means harsh.
I went for the Kings after meeting with the people at my local 4 Wheel Parts store a couple of times and contemplating how to lift my truck for the last 4 years. My number one criteria was that the lift needed to provide a functional improvement and I did not want to lift my truck more than necessary to accommodate 35" tires. For me, this eliminated spacers and most lift kits. I considered Bilstein 5100's, but the 4WP guy told me they were great on the road, but had a tendency to overheat over washboards. I also considered ICON's. The 4WP guy told me that he has ICON's on his truck and is happy with them, but likes the Kings more (which were not yet available when he bought the ICONs) because they provide a more controlled ride over washboard terrain -- which is typical of the So-Cal deserts. So, those considerations plus 4 years worth of research caused me to settle on the Kings. (I hope they don't suck when I really put them to the test.)
The Kings are expensive. Significantly, more expensive than Bilsteins; somewhat more expensive than ICON's. But, less expensive than a Rancho 4" lift, which is the one lift kit that I seriously considered.