The feedback I've gotten, is either that it doesn't change anything at all, or that milk comes from the piercing sites, as well as the milk ducts. Most women do remove their jewelry to breast feed, though others replace their usual jewelry with something very small. This is the type of material often used in hip and joint replacements, and surgical screws. It is silver in color, but is NOT silver. Sterling silver tends to tarnish, and that is essentially a poison to your body.
Sterling silver is too reactive a metal for body piercings.
These are sturdy enough to be durable as body jewelry, yet inert enough to get along well with the body. Not all gold is created equal. For example, 14k gold is 14 parts gold out of 24 parts of metal. Gold plated or gold filled jewelry is NOT acceptable for body piercings. They are very inert and good for wear in the body.