In all seriousness, without even thinking about it being right or wrong, just think about it logically. Yes, short term benefits are (most likely) awesome, but remember, women respond emotionally to sex infinitely more than men do (they can say "NSA" all they want, there really is no such thing).
First, you work with this girl - you cannot have your fun and later cut her off if she get's too clingy. Even if that were to happen and you successfully end things, the constant reminder of the uncomfortable situation remains. Second, she's married with kids - I have no idea what her situation with him is, but it doesn't sound like a divorced/separated situation to me - that makes the whole situation complicated and dangerous from the word go. Who knows how he'll react if he finds out? He knows where she works, he knows where you work. Who knows how the whole family will react if he catches her or if she later regrets her mistake and simply confesses? A minor fling could tear apart a family, it's happened a billion times. And again, you're the bad guy in every scenario, even if she's the one egging you on.
I'm quite certain there are far better situations out there for you (whether "NSA" style or otherwise). Just be patient.
Jason