I have some of those too. Problem is they're nowhere near as efficient at cooling as ice cubes are and never cool my drink enough. It's the melting (phase change) process that does the majority of the cooling with ice cubes, which you miss out on with these solid blocks.
I forget the exact maths, but a quick googling reckons it takes something like 84kJ to change the temperature of 1kg of liquid water by 20K, but changing the temperature of the same amount of ice from 0K ice to 20K water takes nearly 420kJ, or roughly 5 times more energy, which is why they're so much better at cooling drinks...