1. It keeps his water clean all day, without you changing it every time it looks dirty
You changed it this morning and it looked clean when you poured it. By ten there are droppings, soggy pellets and feather dust in it. By lunch it is cloudy. “Thirty minutes after I refill their bowl, it's nasty and smells.”
So you change it every time it looks dirty. And a few hours later, it looks dirty again.
Here is why. You change it at 7am, you leave at 8, you get home at 6. That is ten hours where the only water in the cage is whatever is in that dish, and nobody is looking at it. The problem was never how often you clean. It is the ten hours in between.

2. It ends the poop soup, and gives him somewhere to bathe that is not his drinking water
That one dish is his drink, his bath, where he softens his pellets, and because the rim is a perch, most days his toilet. Four jobs, one dish, all day.
You already tried to fix it. “I just give the birds two bowls and they usually make soup out of one, bathe in the other, and poop in both.” He does not know which is which. You moved it away from the perches and he found an angle.
BirbFlow separates them. He drinks from the moving stream at the spout, and bathes in the shallow basin underneath, in water the filter just cleaned. It stays clean around the clock.
