Product review (5 stars): great for lagering
I bought this to control the temp of my mini-fridge that I use to lager beer in.  Basically you plug this unit into the wall and plug your fridge's power plug into it.  The thermostat probe is placed inside the fridge and basically shuts off the power to the unit when a certain temp is reached.  Because of the way this unit works, you have to set your fridge to the coldest setting. This unit would also be great to turn a deep freezer into a fridge.

Keep in mind if your fridge isn't capable of getting to the temp you set then it will run all the time and possibly damage the compressor on your fridge.  Also keep in mind the probe placement is important.  If you put the probe in the fridge next to where the cold air blows into the compartment, its going to kick off the fridge before the entire compartment has reached the right temp.