I got one of the 4" versions of these for grip training. Overall it's not bad; not perfect, but good. First I'll mention the main thing I *don't* like about my thunder ball: the surface texture, or lack thereof. It seems that the ball is painted with a high quality paint, but it's basically a smooth surface. I think it would have been better to use a powder coat or something similar. I plan on sandblasting mine. I like pretty much everything else about this grip trainer: great size, great price, and, very importantly, the ring where you can connect it to a carabiner is nice and small. I have another size product from another company and the connector is much bigger and can get in the way. Not on this one, though. I'd give it a 3.5 if I could.