Accessory only compatible with the F5 S model. It’s a harness similar to the ones used in Kitesurfing. You have to introduce your legs in it and then it is connected to the SEABOB with a quick connection system. This way you’r arms won’t get tired when using the SEABOB as you are being pulled from behind. You’r arms will only be used to steer the SEABOB where you want to go.