To answer your question, you might consider how the refractometer is used. What decisions are made from the readings produced, and critical is the data? As already noted, even brand new, a unit could produce incorrect readings, so zeroing and calibration would make sense, but since it's just a tool, you really need to understand how and why you are using it and what you are doing with the results. That will tell you all you need.
Cheers,
Adam