Handle with care when frozen.
As the label says, they become brittle when frozen. In practice, that means even a minor shock will split them, a major shock would shatter them to bits. Bare this in mind. I use these to make ice blocks to cool a fanless desktop PC, so I've seen a lot of these cycle. Just treat them accordingly. They do not break down or become weaker when they thaw out. Also good for storing food, if you've run out of old take-away tubs you've been saving.
Great for batch cooking