Let me start by saying I was genuinely excited to try the DOUBFIVSY Pond De-icer for my backyard pond. The promise of thermostatic control and energy efficiency sounded perfect for keeping my koi fish safe during winter.

The floating design works as advertised - it does create a nice open area in the ice. My fish definitely appreciated having this warm spot during cold snaps, often gathering around it in cute little circles.

However, I must address the elephant in the room - safety concerns. While mine hasn't malfunctioned (yet), multiple reviews report melting plastic housings and even fire hazards. This makes me nervous every time I leave it running unattended.

On the positive side, when working properly, it's quite effective at preventing complete freezing in moderate cold. The anti-bite cord is a thoughtful addition for those with curious pets or wildlife around their ponds.

The automatic shut-off feature between 41-91°F seems to work well in normal operation, though clearly some units have serious thermostat failures based on alarming user reports.

Installation tip: Put it in before freezing starts! Trying to position it after ice forms is a nightmare requiring lots of hot water to create an opening.

Durability appears questionable - several users report units failing after just one season. At this price point, I'd expect better longevity.

Final verdict: When it works, it works well. But the potential safety risks make me hesitant to fully recommend it without reservations. If you do purchase, monitor closely and consider a backup solution.