I was looking at these two power balls on amazon and wondering if anyone had any experience. These seem to be the two most heavy duty ones from two different brands, both with the metal cores. I have a little plastic one but I'm looking for something more challenging. I'm curious if the Dynaflex one is worth the extra cost. It has a steel core rather than zinc which gives it more weight but I'm curious if it's worth almost double the price, especially since it seemed to get a few bad reviews on durability and lack of a grip band like the other one. The reviews seem to say the NSD one gives enough of a grip challenge and it doesn't need to be any heavier but I'm not sure the average amazon reviewer trains grip nearly as much as those here.
Dynaflex IronPower V-Power Steel Gyro Metal Powerball - http://www.amazon.co...duct/B003YXZQ5Y
NSD Power Winner's Precision Sterling Spinner Gyroscopic Wrist and Forearm Exerciser with Digital Speedometer, and Heavyweight Zinc Rotor and Stainless Steel Shell http://www.amazon.co...t/dp/B009J0MORY