I saw that too, but I thought it was just for priming. Not sure how it would work if it was hooked constantly to a pump. I suppose that if the power went out and went back on, the return would start filling up the HOB
overflow, and the "priming pump" would also turn back on, re-priming the overflow box.
Now the bottom line is, is it worth $50 more than the other one melosu pointed out? And how much is a priming pump? The one's on Dr. Foster's are close to $100.
Definitely less expensive to just get a thin vinyl tubing to prime the old fashioned way.