They have hard plastic brass knuckles that are made from a 3d printer. ..... I questioned the store owner about their legality and he said, because of the material they are legal.
And the store owner is a member of the Bar? He's done the necessary legal research? And even if they might be legal to have at your home in a display case, what about carrying them around with you?
A lot of people think they understand the law, and a lot of those people are wrong. And a lot of my colleagues have made their fortunes trying to help such folks get out the the messes they could have avoided if they had known what they didn't know.