They last a bit longer than you would think. The original intent of the ice wands was to quickly reduce the temperature of hot foods from very hot, above 165F, to below 70F under refrigeration within 2 hours; then below 40F within an additional 2 hours while refrigerated. Our needs to quickly chill wort far exceed what this item was designed to do. That being said, the process does work, just not as quickly as we may want it to.
Two important points need to be made. First, sanitize! Everything! You can do just as well using old 2 liter soda bottles, the only difference is that the commercial paddles are made of impact resistant polycarbonate. Secondly, do NOT overfill them. My suggestion is to fill the soda bottles about three inches from the top, then squeeze them to bring the water level to the top and then put the caps on, place them in a new plastic bag and put them in the freezer. What this does is allows enough room in the bottle to allow the water to expand as it freezes without splitting the bottle. Putting the sanitized bottle in a clean bag before freezing gives you a barrier from contamination from other stuff in the freezer.
This process DOES work, with a little planning and forethought.
Hope this helps,
Alan