I found shinfin™ fins quite useful, and keep on using to strengthen my kick. Unlike others like Zoomer, the shinfin™ fins do not give me cramp. I found that it also gives me a good cardio exercise, too. Thank you for great invention! I think I was lucky enough to have been able to spot the shinfin™ fins over the internet (just by the luck really), and would be more than happy if more people also discover the benefits of shinfin™ fins, just like me. Keep up the good work.