I can't speak specifically to the KLX, but I've had two Sargent's - one on my DL650 and one on my GSX650F. In both instances they meant the difference between a day of pain, and a day of bliss.
There will be one going on my DRZ in January as well.
OK, but neither of those would have been built on the extended pan they make for dirt/DS bikes. I know folks who have had Sargents on multiple bikes and said their range of experience was from good to shit from bike to bike, so I want to know about experiences specific to this widened pan design.