PetahW,
I looked into doing this, in my shop, but before I bought anything, I asked a friend of mine, who is a professional printer, about it.
The way the process was described is that you start with an ink design on a dissolvable substrate, that will float on still water. This is placed in a tank.
Next, an "activator" or solvent is sprayed over the floating substrate, and that dissolves it, allowing the oily ink to float on top.
Next, you drop in the part, that has had an undercoat paint sprayed on it, of the right background color. No special paint, just the right color. As the part is slowly submerged, the ink uses hydrostatics to stick to the piece and wrap around the part, thus printing the paint.
Next, the part is left submerged until the ink is cleaned off the top, and the the part is removed. Here, he said, you have to make sure to not smudge the ink.
Now, here is the catch that gives it its durability, a simple thick coat of clear-coat paint or finish. The same clear-coat that can be applied over an air brushed image, and the same stuff used on automobiles.
This is an okay process, if you want designs like skulls, or other things on a stock quickly, but I have seen some very talented air brush work applied, that was reminiscent of the old souped-up van days of the 60's and 70's, that will blow you away, and it can be protected the same. I wish I could do the cammo, without stencils, but I'm not that talented. This is why I don't think one is tougher than the other, as you have to protect either image for it to have any wearability.
