Both of mine had a dummy from day 1. Both were breastfed and didn't have latching problems at all. DD2 fed much easier and felt different while feeding, but she liked her dummy even more than DD1, so it wasn't that. I had vasospasms so I think it was a great thing to have a dummy. Once I knew they were full and I was empty, a dummy would let them suck off to sleep and my nipple could relax while I cuddled them.
DD1 rejected her dummies around 8/9 months and wouldn't take them anymore. DD2 goes through patches of not having them at all, and then patches of only at night, and then patches of wanting them 24/7. So that is my only problem with dummies, when they get too old for them but won't give them up!