All pressure assist toilets I've seen are noisey. Not all pressure assist toilet work all that well. Some are known to shread things, and leave little bits floating in the bowl when finished, which doesn't help, since you then have to flush again, wasting the water you were supposed to save.
On Terry's home page are links to some independent tests on toilet performance. Many of the best flushing toilets are not pressure assist. It's all in the quality of the engineering. A pressure assist also requires more expensive parts that are not available everywhere when it eventually needs service.
Personally, I'd stay away from them and use one of the highly rated gravity flush toilets. I've had good luck with the Toto toilets I've bought, they are quiet and work well; plus, they've gotten great reviews.