footbox was wide so foot was unstable in fin.  I timed this fin vs standard "loaners" at my community pool and i got no increase in speed so i dont think that the thrust was anything special.

Requires considerable leg strength just to use these monsters, but adds power to your kick very fast.. However, they do  not duplicate the natural, quick kick you use for pool freestyle.   Difficult to turn in a pool (while training) due to their length.   Use neoprene sox if fins are too big. Really made for open water.  Product quality good.