Regular foot fins work with a very different kick to your natural kick. You can feel the difference. For example, they cause you to slope your thighs down, bend your knees too much and strain your calf muscles too much. Foot flippers imprint the wrong muscle memory for your legs and arms, as well as for your stomach and torso muscles too. This incorrect muscle memory imprint happens because the different foot flipper kick style also changes your arm pulls and your entire body balance. So alternating between foot flippers and barefoot swimming confuses your muscle memory.
So regular foot fins imprint their own, different kick on your muscle memory. You feel this when you take them off and swim without them. It often takes a number of laps to reduce the muscle memory of their different kick, to get back to your natural good kick. Many competitive swimmers know this. So you can see for yourself why foot flippers do not improve your natural swimming kick. They may even be making it worse.
Now you can have fins that give you extra speed and imprint correct kicks on your muscle memory!
See related faq about correct timing of your hip and knee joints.
See all faqs about why hip power fins are the best for swimming.