Thanks everyone for your input. I didn't know it was that much trouble to cut threads. I may re-think buying a lathe for now. What is the most common benefit of using a (low end) metal lathe?
I hope I didn't scare you away from a metal lathe. I like mine, and use it more for pens than my wood lathe.
Things I like:
More accurate
ability for really fine adjustments to diameter
easier to cut metal (kinda obvious I know)
It's just a better tool for custom pens.
Make your own bushings
Lots of new toys to buy
Things I don't like:
Lots of new tooling to buy (actually, it's more a thing my wife doesn't like

) I say toys, she says tooling.
Harder to clean up especially if cutting metal
Some things are harder to do, like most anything non linear. If you want to give your pen a gentle curve to the body, it's much easier to free hand it on a wood lathe. It can be done, but it's easier on a wood lathe. Some people have a tool rest they use on their metal lathe that allows them to use their wood lathe tools. I don't (yet - see above). Many times I'll just move over to my wood lathe for some finishing touches. Plus I do all my sanding & buffing on my wood lathe.
If I had to do it over again, I'd have bought a larger metal lathe. I'm hoping in a few years to get a
Precision Mathews 11-27-VF-LB. I would never have started on that one, but I wish I'd gone a little bigger out the gate.