Instruct: Classify Amazon reviews into positive or negative sentiment
Query: The only one of its kind...

My son was born with a medical condition that requires us to thicken his liquids. The Doc Brown Y cuts are ideal for his feedings. They can be difficult to find in retail stores. The only store around us that even carries them is Babies R Us and they are almost always out of stock. My only complaint is that after about three weeks the opening on the nipples start to widen and this causes the liquids to pour out too quickly. When your paying $6.00 for three nipples and have to replace 6 to 9 of them every three weeks it gets a little expensive. Aside from the widening problem it really is a good product. I know it has helped with my son's feedings. If Doc Brown can figure out a way to keep them from wearing out so quickly it would be a five star product instead of a four.