I have bought one for DD who is nearly 15 weeks old. She's not teething yet, but I just have it in readiness.
However, I'm just worried about the safety aspect of such young babies wearing something round their necks!
For instance, if she's in her cot - is there any danger if she moves her head side to side? She often does this pre falling asleep. Can the necklace catch and become a hazard?