I use these JBJ heater controllers:
Aquarium Heating & Temperature Control: JBJ True Temp Digital Heater Controller
They are more expensive ($80) than the Azoo models ($25). They have a longer (replaceable) temperature probes (60") compared to Azoo (29"). They can be calibrated, retain setting information in power outage and have larger LED
numbers for viewing, and can handle up to 1000w total (800w on Azoo) and uses all digital circuitry (no metal thermostat)s.
When you use a heater controller you plug the actual heaters into the controller and plug the controller into the wall. You then set the tank temperature you want maintained on the controller. You then set the heater thermostats a few degrees higher so that they are always on. The controller then actually sends power to the heaters when the tank temperature needs to be raised. This way the thermostat in the heaters is never reached as power will be shut off to them first. So the heater thermostats are never cycled, never wear out, and cannot stick on (it would not matter if they stuck on anyways).
Personally I like to use to two or more smaller inline heaters as I have multiple canisters on all my tanks and I get better heat circulation. They all connect back to the same tank controller (one for each tank) and that way all the heaters for a tank are always on or off at the same time.
I would much rather trust a more expensive digital heater controller to control the tank temperatures then a bunch of cheap metal heater thermostats that wear out over time. I have never had a problem with these heater controllers in many years of use.