Pressure assisted toilets were/are an attempt to make poorly designed low flow toilets work. They failed the test. While they may work OK for awhile, they tend to break and are extremely expensive to repair. Often the parts have to be factory ordered which means you're without a toilet for 2 weeks or more. Toto did not try to use old full flow designs with less water to meet low flow requirements. Instead, they scientifically designed their toilets to work the way a toilet should work and using less water in the process. In fact, many of the newer models now only use 1.28 gallons per flush. There is nothing wrong with gravity flush, just with some of the toilets that use poor designs.