Suggestions for siphon overflow box

Hi everyone, I'm new to the hobby and I'm setting up a sump system for my 72 gallon saltwater tank. So far I have the sump, filter sock and bracket, return pump and protein skimmer. I'm not drilling the tank so right now I'm looking at the Reef Octopus OB-400 or the CPR CS90 siphon overflow box. Which should I go with or is there another one that is better? I have 2 adjustable flow Eheim return pumps to choose from. One is 260-530gph and the other is 400-800gph. Also does anyone have suggestions on battery backups? I heard this type of system can overflow if the power goes out. Any help is appreciated. Thanks a lot.