The white dot NKT's are a British Military version of the red dot NKT's...it's more or less the same part, think of it like a 12AX7 vs a 7025...same basic job, same basic tone but there are differences.
The in depth deal is this...
For starters white dots were NEVER used in vintage Fuzz Faces, DA always used red dot NKT
The difference sonically speaking is the white dots are a little brighter, slightly more stable at temp changes (but not by much!) and most of the time will get CMPLETELY clean, even with a PAF output bucker where the red dots seem to have a little more grit when clean unless you're rocking all single coils. Also worth mentioning the white dots have a bit or sparkle going on when you roll back for cleans where the reds stay a little darker and fatter.
The deal with the price on the white dot NKT is that Mike no longer has them so at least for right now they are unobtainium...if Mike lands a stash tomorrow the prices will go back down. However on the other hand when (not if but when) he is out of stock on the high gains and the red dots those prices will be goig up too...I have seen all Mikes MKT's go up a few times in recent years)
Also of note the high gain NKT are THE SAME part as the white dot NKT just higher gain...now, they will not get 100% the white dot tone (and the high gains will not clean all the way up due to the extra gain) because being higher gain does change the tone a bit but if you tweak the internal trimmer (not the bias) back a bit and work with it you can get very close to the regular white dot sound with the high gain sound that said I still prefer the red dot.