Does anybody know how the metal printing is supposed to work? Selective laser sintering machines that I've seen all seem way too big to fit in a vending machine.
This one worked by depositing a thin layer of aluminum/magnesium powder over the working base. A laser would then fire, igniting the magnesium which would fuse together the aluminium. The laser draws the shape of that layer of the feature. When the layer is complete, the process repeats for the next layer.
The biggest thing I'd worry about is liability and cost of operation. Because their raw material mix is basically thermite, they have a not insignificant potential to explode during use. While removing parts, for instance, you need to worry about sparks igniting the airborne mixture creating a firebomb. The material is also quite hazardous to your lungs and eyes even when it's not aflame.