These fins are great for developing muscles used in breast stroke kick. The downside is that my coach has all the breast strokers (that includes me) use the fins for 15 min sets and you can get cramps pretty easily. But as my coach says "That means it's working"

Just got and love love them.  Appropriate for beginners and very advanced competitive swimmers.  Forces you to use 100% proper technique and drives hips higher which is otherwise really difficult to feel and learn.  Wish I had these years ago.  Small caveat - these fit me snug which was perfect; if you are on the low end of the size range, I suspect that you have to wear some sort of booties or these will rotate a lot and chafe or be less effective.

I am a swim team coach and this really help 'fix' breaststroke kicks.  

They help strengthen those small inner leg muscles.

I wish you had more sizes like XS, XL, and XXL.

Fins fit well, are comfortable, fit in my swim bag, and make practicing breast stroke so much fun!  I feel my stroke is really improving with this great tool.

These fins have helped many of my swim students become more proficient in their breast stroke kick.  I highly recommend them as teaching tool.  I have also put them on and enjoyed having a more powerful kick.  They're lots of fun.

I read another review and she is a 9.5, the same as me. I ordered the L because she said the M was too big. I am going to keep them, just because some other Special Olympics could use them. I am going to order the M and hope they work. All feet are not the same. So go by the size, not by someone alas.