The data sizes are US woman from the US Human sizes. F = female, not France. On the manufacturer's site in the USA they give the correspondence in European sizes: XS = 35-37 S = 38-40 M = 41-43 L = 44-46 XL = 47-49
For a person who wanted to get back in monofin swimming, it's a good product. However, I am concerned about the quality of the back straps in length. Attention to weight.
Very good transition monofin for those who want to learn: force close to that of palms. I recommend before buying a real monofin. Very nice / no bulb / single threading / lightweight / compact
