Have deliberately opted for a swim fin, which is to open the back, because such "fixed" with a size never fit me 100%. The mechanism to adjust the size is be viable. The closure on the heel is easy to open with one hand, but is absolutely secure in the closed state, so that has solved nothing while swimming. The fins are in size 38/41 approx 50cm long and relatively stiff! I am very satisfied and would take them back!
