Literally the most reliable and longest lasting ato's in the market (they use mechanical float switches vs optical sensors). I bought mine directly from their ebay site and it was $55 shipped. Been running flowlessly for 2yrs.
I know people who have been using this brand ato and have had the same ato for 20yrs.
I forgo any electric or pump fed ATO and use a pair of top-fed gravity ATO units for my 3 gallon and 13.5 gallon tanks. I've been pretty satisfied with how they work and the number of days I get with my covered tanks, about 3-5 days depending on weather/heat.