Aquarium heaters are notoriously unreliable. Some are better than others, but no matter what type you use you are much safer if you invest in a seperate controller either temp only, or a system controller such as a reefkeeper or APEX.
I suggest the seperate controller because if a heater fails OFF, your system will cool very slowly and the contoller will alert you that the heater is not working. On the other hand, if a heater fails and sticks ON your system can get cooked fairly easily.
System controllers can seem pricy up front, but they really are very much worthwhile for all they can do and all the other piecemeal timers and other equipment that you would otherwise buy. (temp controller, PH controller lamp timers, dosing controllers/timers, and on and on.)
Back to the heater itself, it is safer if you get something shatter proof. Again, all aquarium heaters are somewhat unreliable, but if it can't shatter (and release toxins into the water) and it's on a controller, it'll be as bullet proof as is possible.