The purpose of this glass? You can keep your whiskey cold without watering it down. When you order one set ($15), it includes an old fashioned whiskey glass and a silicone mold. You put some water in the glass, insert the mold, then freeze. The ice "forms into a wedge and, similar to a glacier, melts slowly due to the reduced amount of surface area."
At first this sounded like a lot of effort to me, but if you have at least one drink a night when you come home from work, if this is waiting for you in a freezer? That's pretty sweet to come home to. Ya know, if you're into that kind of thing. You can buy a set over here.