SWFA was the only one I know that had it, so I suppose they special ordered a run of them. Many like the "Special Forces" look of the NSN, although in reality the backup sights are pretty crappy. Maybe this was due to customer requests, or just the simple knowledge that the FLR seems to work better for most and that it would be a good idea from a business standpoint. If I had to buy another one, I'd rather get a red full line version over the yellow center-only one.
Its more than just a color change- The TA01-NSN only lights up in the middle of the reticle; The TA01' s whole reticle lights up (or is supposed to- I saw one last week new in box and only the horizontal line was illuminating
). If you look real close, you'll also see that the reticles are slightly different for farther rangefinding with the TA01.
www.ar15.com/forums/topic.html?b=3&f=18&t=228848TA01:
TA01-NSN:
_________________________________________