The guy we get our hay from was over the other day and I showed him my lathe setup.
Being a machinist, the first thing he said was I needed to get a duplicator.
I turn for fun, it's a hobby, and I'm only in the beginning of my turnings (less than 6 months)
I like chucking up a piece of wood and watch what happens when the chips fly.
Typically, I don't have an outcome in mind, just turn and see where it goes.
For me, a duplicator defeats the purpose of turning.
For some of you guys that make lots of calls in any given day or week, I can see where a duplicator may speed things up a bit, if you are trying to make an exact duplicate. If you are turning and selling commercially, I know some folks that want that consistency from call to call. They set up jigs that cut consistant lengths and bore X number of blanks at a time. Consistency if important to them. For me it's not.
I made these without a duplicator.

Just a set of calipers.
I think they are pretty close in size, etc, and yes it took a little extra time to get them that way.
Part of being a custom call is there isn't another one just like it.
If I purchased a custom call that I later found out was turned with a duplicator, I wouldn't care.
It was still hand crafted. You can only do so much with a duplicator.
I guess if boils down to what you are trying to achieve.
It's a personal choice.
Just my thoughts.
Mark