The benefit and selling point of the cup is that it is interchangeable with the bottles and Isis breast pump. However, there is nothing magical about these cups. The spout, for the most part, is leak-proof, but the cup itself is not. The beverage often leaks from under the rim once the cup has been tipped upside-down and then returned right-side up. As a result, I no longer allow my child to handle her own cup, and when going out, I place the cup is a plastic bag (and take a lot of wipes). I intend to replace these immediately with another brand.