The RESTUBE Classic is the most popular model for general use. Likely because it has the option to be worn horizontally or vertically at the hip and includes a small key pocket and whistle.
A common RESTUBE for parents as this makes having a safety device on your waist when needed around ocean currents, rip tides, and general safety. Also ideal for snorkeling to give an added sense of security. Would you drive without a seatbelt? Swim with some peace of mind in the open water. When mounted vertically the bag has minimal drag while swimming. In addition, a whistle and a small pouch are integrated.