Rusty,
A machinist would look at the number of setups required, the precision required, the percentage of material to be removed ("spindle time"), and any special operations. And the size. Working with small parts requires smaller tools and a certain mindset, or it can be frustrating.
Threading is a special operation. Knurling the knob(s) is a special operation. Routinely done, but you need tool changes, and another setup.
The integral knobs in a Fox needle would be the first thing that would go if I were to make these. Just machine a bare needle and press. swage, mold, or solder on one or more knobs. A needle like the Fox isn't particularly hard, but it is ill suited to open setups on a general duty lathe. What you need is an automatic screw machine.
I would also look at rolling the threads instead of cutting them.
The spraybar would be harder if only because there are two threadforms, and an internal precision seat. At least, hopefully there is. Depth control matters. The up side is that brass is really nice to work with, but chip clearance would have to be watched. Again, a perfect part for an automatic screw machine.
But let's be realistic--how many such needles would I be able to sell?
Regarding parts from additive manufacturing. These can be certain metals as well as plastic. The plastics being used are way better than those 25 years ago, before the general public even knew this was being done. For tiny parts, the precision is poor. Remember that you are essentially creating layers of material. The step size of the machine can be small, but you still get the effect. And the properties are still not as good. But golly, it sure is whiz-bang. The Navy marketing people say they can make submarines out of it. Right....
Dave
PS--What a joy it was to get rid of my Fox "spade-style" needle. The constant taper is so much nicer to set.....