I'm not sure this is true at all. A backpack with a frame has more metal than my pocket pistol, as does my MacBook Pro.
Is this system capable of discriminating between various types of metal? I know many hobby metal detectors these days can give you an idea of the conductivity of a buried target, although that can vary wildly based on depth and orientation, and is limited to about a foot or so in soil.
It shouldn't take much to add to a pistol, for instance, to make it unrecognizable to this. In fact, I'd be very surprised if it works well with small handguns today like the Ruger LCP or the Kel-Tec P-3AT.
I beg to differ after examination of the details of the shooting here and the other places he scouted before it. Catching weapons in general is good for any property, but the purpose is particularly to prevent something large scale (the Westgate property in TFA is next door to the LV Convention Center, and at it's busiest will have many crowds coming and going at the beginning and end of each expo day).
I don't know if this tech is the answer. I suspect paying qualified people to do this type of surveillance with video would be more reliable (I've read places like Israel have been doing it for decades), but casinos won't pay up.