The AQQA Mini Submersible Aquarium Heater is an exceptional choice for that really small aquarium.
As always I like the built-in digital display, which offers dual functionality: it shows both the current water temperature and the set temperature.
This feature is indeed "worth its weight in gold," as it eliminates the need for separate thermometers and provides a quick, accurate readout at a glance.
One of the most commendable features of these new heaters is its alert system. If the heater fails, it emits a loud beep.
The durability and performance of the AQQA heater have been so satisfactory that I have replaced more expensive, well-known German brand heaters with these in all the tanks in my fish room.