EHEIM JAGER Aquarium Heater 150W (13 Inch) - Submersible Fish Tank Heater for Freshwater & Saltwater - Reliable Temperature Control for Home & Office Aquariums

They work. Read and apply the directions and they perform well. They are not the easiest to calibrate but once dialed in according to the product instructions... they are solid performers. It may take a few retreads of the instructions and patience, but they do work. A long time user. Mine eheim heaters always outlive the suction cups, helps wash cups and clean glass occasionally. Buy an extra eheim hanger, 7$ , I think. Best of luck from Michigan.