I don't own a NSN model, but I did borrow one from a friend for two weeks (hell of a friend, wouldn't you say?
). I ended up buying a TA-01 instead. The red reticle was a lot easier to see at night for me. At the time I bought it there were a few threads about the TA-01 vs. the NSN and it seemed most people preferred the red of the TA-01 to the amber of the TA-01NSN. Of course, YMMV. A lot of people also don't care for the chessy back-up sights on the NSN.
Finally, many people (myself included) much prefer an ARMS 19S or LaRue mount instead of the NSN's mount. I didn't want to pay extra for a mount I didn't really like.
Last weekend I finally got to shoot my TA-01 at night. It was at a machinegun shoot. Even with some small fires downrange and a flare or two, I could pickup the reticle in complete dark, on a fire (it is then a black reticle again) and even in the shadows near the flames. I wonder how the amber of the NSN would have compared in the shadowy areas close to the flames.
Hope this helps some.