Owen had one from about 2 weeks and didn't cause any probs with bfing. He only had it for naps and bedtime. He rejected it at 8 months old when his top 2 teeth came through at the same time and totally refused it, looking at us like 'what are you putting that in my mouth for??!!' Was a tricky few weeks but he's doen the job for it we dont have to worry about how and when to take it away!!
We only every used 'soother' type ones with flatter ends, not the biggish ones.