I lost mine dammit and I'm pissed. I have a set of very, very nice, new 14's coming from TNVC and I loved that thing. In the Army, they were generally a piece of gear like the skullcrusher that wasn't normally issued unless asked for. So not many folks had one, and even of those that did, not many used it. But I used mine, I didn't like getting lost and I was good at land nav.
It has its own set of limitations, hard to describe, but basically you just see a small window in the peripheral of the NOD, usually up top I think, that displays the degree of your heading. It is really nice once you get used to it, and it does have a multitude of uses. For navigation though, I still keep a good old Cammenga tritium compass on me when I go out regardless. And a backup for extended stays.
In addition to above uses stated, if you say, set your heading on your map using your compass, then when trekking in the dark with NOD's on, the little compass can easily help you stay on track without constantly stopping and looking. I loved 'em and that was the number one reason I used it. That is why I'm pissed I can't find it!
Take care, and don't lose it. It is expensive as hell and it is just a little piece of black plastic.