My interest is in training fins to help me develop my underwater dolphin kick, so these comments may not help you surface swimmers out there. I started with second-hand Speedo biofuse fins which were very powerful and noticeably developed my quads. However, they started to split, and the newer ones come in a smaller selection of sizes which are either too big or too small for me. After trying several other brands I settled on Maru which are super comfortable with a good range of sizes and non-chafing, but maybe not as powerful as the Speedos due to their flexibility. I hoped these Arena fins would be stiffer in the fin area which they are, but they are a looser fit with sharper edges around the toes and give noticeably less thrust on the up-kick probably due to the lack of side strakes/vanes on the underside, so I'm going back to the Marus.