In the past, I have noticed a reluctance of frame shops to want to add a great length of threads, and they charge by the inch, 20 dollars at last count.

The tools can require frequent, expensive re-sharpening, patience in use, and a skilled operator.
Starting threads where none exist requires a lathe or screw machine, so extra expense there.

Now that I have a 1" die and handle (out past Sacramento) I seldom use it, but it did a nice job recently of cutting usable English threads into a French steerer.

I would be reluctant to apply my own die to any threads that had been "worked" by a dull cutter, since there is a hardening that occurs.