What exactly is the 350 GSM material, is it more of a paper/cardboard, or more like a plastic? I like the concept but Im not fond of paper materials that tear. Making the stands for the targets could be on the annoying side too, though Im sure I can just make stands out of my K’nex parts.
Another thought, have you tested the targets to see if Boomco darts stick to them? If they do, are they sturdy enough to survive the dart being pulled off?