I am running an overflow on my 135 setup. First I ran it as freshwater, and now as saltwater. It has been running for about a year with no problems.. Yes the power has gone out several times here. It is setup with fail safes to never overflow.. even when the power goes out..... and will continue to work when the power comes back on. All of my drain pipes are glued, my sump has enough room for draining water for when the power goes out, and my return power heads have vent holes drilled to stop any suction to prevent back-flow. It is not rocket science and I think that everyone that has had trouble with one just has not had the patience to set one up properly.
Drilling the tank will be a much nicer setup though. You better make sure the tank is not tempered though. If I ever have to drain my tank for some reason I will most likely drill it. I didn't drill mine to begin with because the overflow option was easier to pull off for me.