NSA or FWB never ever work!
Usually they end with one party having feelings for the other, or both parties having feelings and then it complicates things especially since they went into a FWB relationship because they didn't want to be in a relationship in the first place! But that's never the case. If you have sex with someone, it will always become intimate one way or another. Or at least one person will develop feelings while the other may not, and then the FWB connection is ended. Or they might just end up dating, or just call it quits before it happens.
There's several outcomes I'm sure, but my main point is that they always end up in weird or awkward situations. Sex is sex people, it's an intimate act. It messes with people's minds sometimes, and so does FWB or NSA. Somewhere down the road things are going to get weird for both parties.
It's happened to me three times (Fool me thrice, I'm a friggin idiot) and a few other people I know of as well as stories I've heard from others people about how someone they knew had the same thing happen. It just doesn't work people, or maybe I should say "It generally doesn't work," I just say that because maybe there is a FWB couple that have worked it out.
But I highly doubt it.
Only people with money say that money doesn't matter.