The purpose of the DC4 and DC8 is to eliminate the problems often seen when using X10 modules to control lights, heaters, etc. X10 passes control signals through the 110 volt house wiring. There are all sorts of things that can interfere with these control signals, sometimes resulting in the aquarium equipment failing to turn on or off. The direct-connect modules have built-in relays and control circuits to switch devices on and off. They connect directly to the AquaController using an RJ-11 (telephone) cable. Because the control signals do not pass through the power wiring of the house, there is no risk of the control signals getting lost because of electrical noise or other interferences on the electrical lines.
The bottom line is that the direct-connect boxes (DC4,DC8) should be more reliable than X10. They certainly bear little resemblence to a power strip or surge suppressor.