A local suspension tuner recommends them (bleeders). For whatever reason he was unable to put them in the KDX forks. Amounted to some fitment issue...don't recall what it was.
re: on the trail
I regularly bleed mine. Not too handy having to use a screwdriver. Do it anyway.
Are the kdx screws 5x.8? Does it look to you like a socket would fit OVER the release button? The shorter of the two options (the 32 tpi one) would be hard to fit in the recessed cap if it didn't.