Dolfin pull buoy for swimming technique

Dolfin Pull buoy kick ball "Dolfin's pull buoy kick ball is a versatile tool that is placed under the chin, between the knees or in the hand to help improve the swimmers' different techniques. The kick ball is the only equipment on the market that improves knee positioning through the breaststroke kick cycle" https://www.aquam.com/en-ca/pull-buoy-dolfin-kick-ball-tr--26045 pandemic purchase Used a few times I liked it best in the hand or between the knees. Could not hold on to it w my knees for breaststroke though!