CrazyFly fins are Razor sharp and designed with a very thin profile to cut easily through water, prevent drag and make the boards faster. Razor fins also provide flex to some extent, which allows for comfortable carving and transitions. Lots of R&D has been put into invention of this incredible material.
Later models have more rounded edges to enhance safety and reduce the risk of cutting your kite. Just in case you are still one of the people who use their board instead of a sand bag.