Product review (3 stars): Nice idea, but awkward design
I like the idea of seeing what your freezer is up to  I have an older fridge/freezer and suspect that it is not always consistently keeping items in the freezer at the right temperature. Sometimes ice cream looks like it has thawed a bit and refrozen, as well as fruit stored in the freezer. That is a big concern for items like meat! The design consists of a test tube you fill with water and a lid and straps. The directions are clear, and the tube itself is sturdy. The meter is a marble (amateurish), and the straps to attach the tube in the freezer include a rubber band (unprofessional, and it stretches out and distorts after being in the freezer for a while, which allows the tube to tilt) and a velcro strap (more appropriate, but allows the tube to tilt because it is hard to keep it attached securely once the tube is frozen and slippery). The idea behind the meter is that once you have a block of ice in the tube, any thawing will allow the marble to drop down the tube, therefore showing you that the freezer is not maintaining a consistent temperature. I would be very impressed with this as an amateur science project, but would prefer a more professional set up. It does work though, but constantly readusting the slipping tube and replacing the rubber band is annoying. Improve the design details and you have a handy low tech item that works.

Keep in mind, however, that this meter won't show that your freezer is warmer than it ideally should be, but under the freezing point of water in the meter. For example, your freezer may be 25 F. It should be around 0 F. The meter will, of course, stay frozen and not move.