I have seen very few use it personally, but I suspect the best tanks do. Most drilled tanks are sold with 2 (Herbie or a variation) or 2 in each overflow that I have seen, although the smaller return pipe could be converted to a 3rd drain pipe. And most bean animal systems I have seen have the durso air opening such that if the primary fails, if the secondary can not handle the flow, it can convert into a syphon at high water levels when needed to prevent overflowing. I believe it started because many people believe the emergency drain should have no flow under normal conditions. Bean animal showed people how he did 3 pipes and why it worked. But to keep a syphon always going, it appears easiest to shut the valve until you barely get any flow into the secondary overflow. The full syphon is then silent because it pulls no bubbles (and you get no salt creep to boot). Too close, and you have to adjust more often. The trickle down the secondary isn't enough to cause slurping or pulling in bubbles. Red Sea tanks I have seen use 2, but the primary is not a regular Herbie (2 pipe). I believe the Ghost Overflow is designed to be a Bean Animal Overflow. With 3 overflows, it is thought you are less likely to have a failure due to redundancy (such as when a bubble tip gits in the overflow, or snails, or kori. Remember, if you have a small overflow under a syphon that is almost open, a emergency overflow of the same diameter may not be able to handle the flow, or at least quick enough to go into siphon mode to prevent spillage. I have a HOB the has repeatedly overflowed when started as the drain doesn't start fast enough.So do most hobbiest use the bean animal because it has three drains?
Since Marine Depot is on this chain, I was wondering if they knew why the Durso (Secondary Drain Here) has larger diameters on top and necks down just above the bulkhead? My 2 guesses are that: complete 180 turns, as found in many Dursos, are waste, Drain and Vent items and those usually come in larger sizes (2"); or the funneling helps keep the air from traveling down with the water, creating a cone of air in the tube.These diagrams were made for sharing, so thank you so much for passing them along!
Here are couple of links NJR members may find helpful:
How Durso, Herbie, and Bean Animal Overflows Work - Marine Depot Blog
How to Plumb a Sump - Basic, Intermediate and Advanced - Marine Depot Blog