SilencerCo bills the Maxim 9 as “the world’s first integrally suppressed 9mm handgun that is holster-able and hearing safe with all types of 9mm ammunition.” Essentially, the barrel itself is a suppressor that significantly reduces the noise generated from firing the weapon, and therefore better helps preserve the hearing of those firing it.
There are a bunch of YouTube videos showing the gun being fired, such as this one by Iraqveteran8888.