When I was doing my OW dives my calf muscles were cramping up so badly that I thought that maybe I wasn't cut out for diving. An instructor who was along for the ride lent me a pair of his Force Fins to see if they would help. Immediately the cramps went away. That evening I bought a set off of Ebay for about 25% of the retail price. After using them for a while I realized that I needed a pair of inserts because they were rubbing the top of my foot and the bungie backstraps. (I don't like or use booties.) When I am in the water I let the straps drop and not make contact with my heels. They stay on even though they are not strapped on. I wouldn't be without them.