These plastic flasks will protect your alcohol from any prying authorities who want to upcharge you for beverages. Flasks Are Non-Metallic & Cannot Be Detected By metal detectors.
The reason for this curve is simple: so that it can easily be pressed against one's body so that it is better concealed. A curved flask fits better in a front or back pocket as it will press against one's leg or thigh. Even a flask that is kept in someone's boot or sock can be pressed against the leg well.