There has been horror stories with U tube overflow boxes. I have been using them on two tanks for a couple years. If the tank and sump are set up to handle the overflow amount, you will not have a flood. Mine are set up so that if the return pump stops, the tank will continue to flow into the sump until the water level falls below the top of the overflow box. But my sump is large enought that it will hold that water without overflowing. The sump is also set up so that if the over flow U tube looses syphon the pump will only pump so much water into the tank and there is room in the tank to hold it without overflowing. Unfortunately that means the pump runs somewhat dry. Thats why I also use Eheim pumps for the return. They do better than most when they run dry. And they dont run completely dry. There will still be a little water in the return section.
If it were me!!!!
What I would do is use the Eshopps dual overflow box, (get an extra U-tube just to have when cleaning the others) and an Eheim 1262 pump. 40 gal long or 40 gal breeder tank for a sump and build in 3 sections. One section for the skimmer, one for the refugium and one for the return pump area. Return pump area holding no more than 4 gallons. I would also put a T in the return line with a ball valve off the leg of the T so that you can hook up a reactor, whether carbon or GFO.
Here is a great site for figuring out how a sump works and building one.
