I purchased this fin in March of 2000 for fun, and I still use it occasionally after all these years! After it arrived, I realized I was in-between sizes, so I ordered the footbooties, which work great! Back then, you could choose between different stiffness levels. I picked competition stiffness figuring I’d regret it later on if picked anything softer. Once you become conditioned and comfortable with it, you can corkscrew, change directions, and even pop straight up out of the water past your knees. It’s amazing how much speed and force you can generate! I don’t think it’s intended for butterfly stroke training, but it helped me tremendously in that regard. I recommend this product to anyone looking to improve strength and technique, or just looking to put some extra fun into their routine!