I ran 3 DT's for several years (125g, 100g, 90g) and ran multiple units in their sumps. Only 2 systems had chillers. I think I ran twin 300w in the 125, dual 250 in the 100, and dual 200 in the 90......However since I got started in the hobby I've had 2-3 heaters (run away) and basically never shutoff suddenly one day - and luckly the chiller kept the reef from cooking off - cause I noticed the chiller was running ALOT during the winter - when it about never runs.....found the darn heater would just run - regardles of temp setting - as long as it was plugged in. I've used several brands of the generic heaters - (marineland, ebo-Jager, even cheep pecto brand for 20g qtine tanks) and over time - I think about any heater can "fail" in a constant "on or off" mode - or at minimum become unsteady over time.....The high dollar computer-controlled units am NOT familiar with, as I just replace my heater units about every 2-3 years anymore - regardless of how they are working....
In the 475g I run 3 300w units in the sump, but have not really seen how it'll perform when its "cold" in the house yet - cause I only got in running march of this year - so I may need to add a little more heat - BUT it has 2000 watts of MH & HQI lighting over it and THAT adds more heat to the tank than a couple heaters.