I went ATO free for 3 years and just last week got my first one. Main reason being I'm going on my honeymoon in a couple of months, and I wanted to be able to only have someone come check on the tank every few days, instead of every day, especially if they were just stopping by to add a gallon of water.
Recently I've just been adding water to a tape mark once or twice a day, but in the past I'd made a pressurized 5 gallon water vessel with a needle valve that dripped every 5-7 seconds or so into the tank, and maintained levels perfectly for a week at a time, with maybe one adjustment a week. This was nice, and cheap to build but not without it's problems. First, I was the only person who knew how to set it "just so" so it would work well. It did take a bit of work to get it adjusted when I did. Also, there was no fail safe for this. If my needle valve failed or air pump for pressure failed the tank could get 5 gallons of water at once, or stop getting topped off.
I now have my first ATO with a 5 gallon bucket, and so far I am enjoying the convenience, and I imagine the coral may like the more consistent parameters than me topping off manually. I'll just have to be diligent about keeping the float switch clear of salt creep and other buildup.
