My mum suggested these to me in the early days of nursing as she suffered from flat/inverted nipples as I did. These don't use suction, as some have misunderstood, but pressure to gently make your nipple more pronounced.
For me, they were a godsend at the beginning. I had one flat and one inverted nipple. Using these kept my nipples from going back to their natural flatness between feedings, making it easier for my baby to latch on to the next feed. The holes keep the air circulating, which is great if you've suffered nipple trauma and need to keep you bra off the skin. A bit of lanolin and we healed much faster. The downside of the holes is that you can create quite a wet spot on your shirt if you have been leaking milk then bend over! I used breast pads whenever I wore these to help absorb any leaks.
I wore these nearly every day for 2 months , sterilised them overnight and boiled them every few days. They held up well to regular use. After about 2 months we no longer need them, they did their job and baby did his so I've got easily latchable nipples now! ;-)