Asides from ejecting casings and a bit more noise and slight recoil (and paint... but I seriously doubt that was the selling point anyone is pushing), isn't this basically a really souped up airsoft gun in the end? Or am I missing something?
I mean, if you're going to be wearing the level of protection you'd need to wear in order to use simunitions, you might as well just shoot .29g BBs @ 450fps, you'll get that range and accuracy.
The rest is novelty. And even there, look at the KWC Mini UZI, that thing has amazing recoil.