heater failure is the most common disaster in this hobby, and more worse heater failure in ON position on top of that.
if you go with a little less watt heater but more in qty. this helps such disaster.
say if you have 3x100w heaters in a 120gal tank. one heater messes up and stays on and you dont catch it or not home etc, itself alone will not be able to boil your tank out while ur at work and return. Also if its backed by a controller then power will get cut off and thus causing no damage.
if one heater fails to turn on then u still have other heaters to atleast keep up the temp.
So heaters in this hobby are critical. i strongly recommend a controller and then few smaller heaters than just 1 big one.
By the way thanks for bringing the dead thread up over a year. lol its a good topic though