US$ 28.64
b12 injections intramuscular or subcutaneous What Happens If You Inject Into Fat? · SQ vs. IM · PA Relief Best Vitamin B12 Injection Sites
Description
Here's the simple comparison

The break is not required for safety or receptor resensitization, but it allows for reassessment and prevents indefinite use of a compound with limited long-term human data

Are There Side Effects
Children and teenagers : no safety data exists
Protects against mislabeling and ensures you receive precisely what was ordered

Being me (sciencey minded) I've done my own trials on myself with in-date and out-of-date ampoules and found no difference