In general, pressure-assisted toilets work better than gravity models. These toilets use in coming water to compress air in a chamber inside the tank. (A water pressure of at least 20 pounds per square inch is required.) Flushing releases this compressed air in a burst, forcing water to prime the trap almost instantly. Air assist allows the tank to operate with less water, making more water available for bowl. More water in the bowl means a larger water spot and cleaner bowl. And finally, the tank-within-a-tank construction completely eliminates tank sweat caused by condensation during hot, humid weather.
With these advantages, you'd think everyone would want a pressure-assisted toilet, but that hasn't been the case, the most common complaints are that they're too noisy and too complicated. Starting each flush with a burst of compressed air does make them noisy, and they're certainly less familiar. Most people would recognize the tank components in a traditional toilet, but lift the lid on a pressure-assisted unit, and all you'll see is a sealed plastic drum, a water-inlet mechanism, a hose, and a flush cartridge. Most manufacturers use almost identical tank components.