The one I have works really well. Watch Uarujoey's video on YouTube. They are easy to build. Works great the pump I have now is only 240-300 gph and I need a bigger one. Just bought a 180 gallon tank and I will build a double overflow for it.
So after watching a couple videos I think I'm going to try and build one this next week. My tank is 135g with a mag950. You think 2 1 inch overflows will be enough? Where do you get the small check valves at? Do you glue them in?