I bought the blue one because the hardness range was wrong on the website, the black one is harder. On the fifth use, one of the holes started to tear without me ever putting both hands on it (it tore with the force of opening the fingers!). It helped with my injury, but for its price, its durability is very low. I didn't try to use it as a hot water bottle at all, and if you're not injured enough to need this feature, maybe it would be better to buy something else.

I got it to strengthen the muscles of the forearm and wrist due to a tendonitis that was bothering me. It helped me a lot, I would gladly recommend it