It depends on your loading practices. If you only load large batches from time to time, then readjusting the die may be of no consequence to your time. If you run one right after the other and with greater frequency, you may prefer to keep a separate die so you can switch it out quickly.
More commonly you find people who load both .38 Special and .357 Magnum or both .44 Special and .44 Magnum who are having to make that same choice, because the die sets for those pairs are the same. I have acquired separate die sets over time, but since my volume of revolver ammo was never nearly as large has my volume of other cartridges, I can't say I really needed them. It was just a matter of running into sale opportunities at gun shows. You may want to take that same opportunistic approach if you are in no hurry.
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