Like all of the best ideas, this is remarkably simple.
The problem with cooling your favourite spirit with ice is that it gradually dilutes the liquor, changing the taste and the strength.
The solution is to use non-porous soapstone cubes which are previously chilled in your freezer (the recommendation is for 4 hours). Put 3 of these into your glass, cover with your drink and leave to chill for 5 minutes. Then drink, savouring your favourite tipple chilled but not diluted. Perfect! Once you have finished your drink, you then rinse the stones, let them air-dry and put them back in the freezer for next time. (The safety-conscious instructions warn you not to chew the cubes...)
The kit comes with 9 stones and a small drawstring bag to hold them in the freezer. Of course, if you like to drink swiftly, or have friends round, you may need more than one set!