3D printing is pretty expensive for mass production and for the price of a good printer you could cover a good fraction the cost of the mold for injection molding. After that the actual cases are pennies a piece.
So it boils down to just how massive do you expect your mass production to be? Is it hundreds of units, or tens of thousands or millions?
Recently I've seen a very expensive 3D printer (full colour binder jet) and while the finished item is a nice toy with working interlocking gears, the surface finish was definitely not what I would like to see on a final product which is supposed to have a professional look.