Hi there Judy
Every so often I get a spate of mothers (collective term?) using nipple
sheilds. They seem to be given out by hospitals when the problem falls into
the "too hard" basket or they want to discharge the mother.
In my experience "some mothers" find a nipple shield helps them over a
difficult period when a baby has trouble attaching, however I strongly
suggest they only use one for a few days, so they don't have problems with
milk supply or the baby  has a chance to get too used to the sheild.
some mothers seem to have a good supply and the sheild makes no differance,
but many babies really don't go back to the breast very easily after using one.
Bottom line is I avoid using them except as a last resort and then get the
baby off it as soon as possible.
Jackie