I believe NKG's are a quality plug, but most everyone here uses Motorcraft or Autolite plugs. There are many threads about problems with other brands of spark plugs in Fords (especially Bosch plugs). I don't recall every reading where someone had problem with NKG plugs, but not many have reported trying NKG's. I use Motorcraft or Autolite double platinum plugs in all of my Explorers/Fords. They work very well, so I figure why use another brand and take a chance?
Note: Due to Ford's "wasted-spark" ignition system I find the plugs on the driver's side wear down much worse than the passenger side, If you develop a miss near the end of the recommended service life of the plugs, it will probably be the plugs on the driver's side causing the problem. For this reason I change the driver's side plugs at around 50K-70K rather than waiting for the miss to happen at an inopportune time. The last time I had an issue ("misfires on multiple cylinders") was on my daughter's '00 Mountaineer 5.0L. At 80K the driver's side plug gaps were so large I couldn't measure them, while the passenger side plugs were maybe at .060 (originally gaped to .054) after 80,000 miles, which is a negligible amount of wear and would have easily made it to the recommended 100K change interval. I've seen a similar amount of uneven plug wear on SOHC V6's.