This is my 2nd winter using this item.  I use in to a 4 X 8 duck pond.  The pond is roughly 2-3 ft deep.  I put this heater in a bucket with a rock or 2 and sink it to the bottom of the pond.  This item works great.  I am in Maryland and today it is -5 degrees and my pond is fully open with no ice and my ducks are happy.  This worked this year and last year and i would recommend it for keeping a pond open during those freezing days where your animals still need access to water. 

I bought one of these a few years back and I can say it works great but requires a lot of upkeep. The aluminum design submerged in water and having an electrical current causes calcium lime build up. It sticks to the heater causing hot spots and gets lime settlement in the bottom of your tank. To clean you have to submerge the de-icer in vinegar. This will eat away the lime deposits and you will still have to take a wire brush to get it all off. Once your done put back in and the lime starts to build up again. However, the water never froze. Cord eventually wore out causing an electrical current to carry through the water.