A UPS inherently has automation built-in. It detects a utility electical outage and resumes electrical output to an attached device, such as a water pump. This is key when no one's home. A battery-operated air pump obviously needs a person to set it up during an outage.
Again it can be 1 circ pump hooked up the the UPS to get the water moving. It doesn't have to be a 50W 1.0A return pump.
When factoring in the cost, the (subjective) perception of value comes into play, making air pumps more attractive, IMO.
WRONG!!!!! :fight2:
The air pumps ALSO auto start when there is no power! I have them always in my tank(even though not all my tanks-I just got too many)
There is a switch on the top(ViaAqua DC250) to tell it to auto start when power is out.
You have to get the right one, they are designed for power outage just like UPS.
Cost me $7.00 from Wavepoint in MACNA, retails $9.00-$11.00. You put one in the sump and one in the display tank.
The major draw back of this type of backup is it does not handle canister filter nor calcium reactors. Neither will the UPS when they run out of the juice.
During the last couple months, many tanks in the tornadoes stricken area of mid east, survived simply with the battery air pumps but those with UPS cannot do anything, they don't have batteries for UPS and the first day after the tornadoes, ALL generators are sold out. They do have DD batteries

. If you are active over fish forums over those area such as Kansas, Missouri..., you can see how many people are praising such low cost solution solve the most disturbing tornadoes torn area for days and even week.
The most important thing is that it lasts more than a day with just two batteries. Most UPS implementations hardly run more than 4 hours. If going UPS route, I would do what Warren did, a marine type battery with inverter. That will buy you a lot more time than regular UPS. Of course, it comes with a price too. Most implementations cost over a thousand. Even with such battery backups, I will still put my air pumps in my most loved tank.