I use multiple Visi-therm classics and Visi-therm stealths. I never had a heater fail in the off position before. When they fail for me they fail in the on position or leak (and short out). I have several heaters on my current system, one in the sump, overflow, fuge and frag tank all controled by an Aquacontroller. Controlling several heaters at once is a nice benifit of X10 and the Aquacontroller.
Another tip for those of you using a secondary controller to run your heaters: set the built-in thermostat on your heaters to 1 or 2 degrees above your controller's temp setting. This way, if your controller fails with the heaters on, the built-in thermostat will cut off the heater before you cook your tank.