There was one company, Ripplin (basically a big MLM scheme) that did this, as a "look how special this is". If you then invited a couple of other people (without being able to say what it is) you got to the next stage. They did make it though, so that the NDA was to see a youtube video, which was a public video, so could easily be found on YT, it'd just make the average user feel like they'd been invited into something special. It worked, and they're doing well. YMMV though, what works for a scammy bizopp may not work for you.
