I remember visiting this website once...
It was called Mermaid Tails によって Fin Fun | Get a Real Swimmable Mermaid Tail または 鮫, サメ Fin
Here's some stuff I remembered seeing:
❝... it propelled her to be more active ... and really helped her with core muscle development. I would definitely buy this again!❞
❝The design is amazing and in the water the skin looks so real! I was wary of this tail at first because the "fluke" monofin looked too small for my preference.let me just say that this tail swims perfectly! It is the perfect size! So in love with their monofin design very comfortable! I underestimated this tail!❞
❝My daughter...had issues in the water, for instance she always held her nose ...But fin fun just changed everything. She knew! She loved her tail and took to the water like a mermaid in it from day 1...She is now an excellent swimmer! THANK YOU!!!!❞
❝When she first got into the pool with it, I was so nervous. I insisted that she wear a life vest...After a few laps, we let her take off the life vest...She said that it is actually easier for her to swim with the tail than without it.❞