After getting horrible cracked/bleeding nipples the first 3 days after my son was born (he was a chewer!), I sent DP out to get nipple shields as I wanted to persist in bfeeding but my skin needed a bit of a break. We were still in hossy at the time, the midwives told me that nipple shields shouldnt be used, that they will confuse bub, and ill never be able to b-feed properly.
By 9 weeks we had gradually weaned of them and strait onto the boob, it was a learning experience, but DS and I figured it out without too much hassle. I continued to breastfeed up until he weaned himself at 18 months

Im not saying nipple shields are for everyone, but they definitely have their place, and I would not have been able to feed my son for as long as I did without them