DD1 had one til 6 months, but was FF from 6 weeks. Dummy made no difference to us.
DD2 refused from the start, even though she had colic & needed it!
DS had one from a few days til 4 months. He was BF til 23 months, so it caused no issues for us.
I've given DD3 one on occasion, but she's not too interested in it. Hasn't really needed it.