I have no experience with replacements. Mine worked when I swapped out the air suspension for conventional springs. The ride height sensors are locked up now though from several years of sitting still I guess they corroded. Aside from Ford which may be a bit cheaper from TascaParts.com than your local dealer, I'd try a brand from RockAuto.
Alternatively, you could consider turning off the air suspension and replacing the air springs and struts with conventional springs. I put in the Rancho Quicklift struts in my '04 and have been very pleased. I also got basically no lift out them in the front and a little in the back. Handling improved, load leveling was lost, reliability sky rocketed and cost to maintain plummeted. In my book a win.