Look for useful variety
A pack with more than one length can cover broad running stitches, small corners and layered repairs. The exact count matters less than whether the options solve different problems.
Check that the pack explains length, eye and intended use. Vague descriptions make it difficult to repeat a successful pairing later.
Check the thread range
The eye should accept the sashiko thread you plan to use without crushing it. If you also use fine thread or Kogin thread, make sure at least one needle is suited to that scale.
Thread each candidate and make a short swatch. A pack is useful only if the needles feel smooth in your actual hand and fabric.
Store the pack as a system
Keep the original size information with the needles and mark which one you prefer for each cloth. This turns a beginner pack into a working reference instead of a mixed drawer.
Retire any needle that becomes rough or bent. Starting with a clean tool makes it easier to tell whether a problem comes from technique or equipment.