Here is a blurb from the site:
Hazelwood has the medicinal property of neutralizing the body's acidity. It is an ancient remedy first used by aboriginal people to reduce their babies' teething pain. It relieves or prevents ailments such as acid reflux, heartburn (great for pregnancy!), eczema, rashes, constipation. In order to receive the full therapeutic benefit, the necklace must be worn as much as possible.
A parent I know was telling me about them, apparently they are popular in Montreal. His brother sent him one and they believe it helped their son with constipation. I was hoping to hear others who found them useful.