Depending on what you are keeping in your aquarium, a heater can be very essential. Some tropical fish such as Bettas need a heater to thrive. Shrimp on the other hand like the cooler water and will not do well with a heater unless you are keeping Sulawesi shrimp.
We have several heaters to choose from depending on the size aquarium you have. Some are preset for ease of use and others are adjustable which are a must for Sulawesi shrimp who need a higher temperature. The Fluval E Series are my #1 choice to use with my Sulawesi shrimp.