The thing about the 3-D printed ones though is that it seems like it would be easier to design and manufacture more 1-offs, customized to the needs and abilitie

The thing about the 3-D printed ones though is that it seems like it would be easier to design and manufacture more 1-offs, customized to the needs and abilities of the user; whereas the more traditional prosthetic device will be designed, necessarily, for more general usage. The one fits the needs of an individual; the other only kind of fits the needs of the individuals in a group. I would say for this reason alone, 3-D printing is a very exciting advance.