I used nipple shields for the first 5 weeks with my little boy. He was quite small and his mouth therefore too. His tongue didn't stretch out over his bottom gums, so breastfeeding was excruciating. He also had a tongue tie snipped after birth. It made it possible for me to feed him how I wanted and establish my supply. The first 8 weeks are crucial for your milk supply, so I would recommend the shields. They are a bit of a faff with putting them on and sterilising them, but it made feeding pain free. I then dropped them after 5 weeks...first one side, then a day later the other. I was quite nervous, but it worked. The thing is that baby does have to relearn how to latch again, so be prepared for that and be patient. But now, at 10 weeks pp I am breastfeeding still. Good luck!
My baby is 5 months next week, I began using nipple shields when she was a couple months old because of nipple pain and unfortunately she is so dependent on them now that she won't nurse if I don't have it on. We got the tounge tie released so I was really hoping to be able to transition her off the shields but haven't had any luck yet. I know this isn't the case for all babies though, some are able to transition more easily. I personally regret ever using the shield and wish I'd just deal with the pain or done the release sooner and worked with the lactation consultant to improve her latch, before she got dependant on the shield.