Product review (4 stars): Easy to set up and use.
We just bought a new refrigerator and I wanted to be sure that the freezer was working properly so I ordered the Freezer Meter Frozen Food Safety in Seconds gadget.  Set-up cant be faster or easier.  Fill the plastic tube with water to the designated spot on the bottle and put the meter into the freezer to freeze the water.  Then place the small plastic ball on top of the now frozen water, put the cap on the tube to prevent the ball from falling out, hang the tube on any convenient place in the freezer with the Velcro straps that are attached to the tube and Voila, good to go.  If the freezer dips below freezing for any appreciable time, the water in the tube will unfreeze and the ball will drop to the bottom of the tube.  Cant be much more basic than this concept.

The manufacturers tell us that: this device is designed to work with freezers of all shapes and sizes and the installation is simple -- your freezer protected in minutes.  They also say the device is scientifically proven to provide reliable information every time and the device is small enough to stay out of the way.
Of course, I won't know if the device actually works unless my freezer stops working, which I hope won't happen.  That said, I think this freezer meter will work as advertised.