Not quiet but nearly. It feels great in the hand (I have large hands) and all the buttons once you get used to it are in the right place, the only problem is the ball is not as free as it should be, I have tried other makes and though it's slight it's not as good as it should be, a little sticky on small movements, not a deal breaker but not ideal.
The ball works well, provided you keep it and your fingers clean. The software is easy to download and provides lots of options for the buttons. It arrived from Japan without extra costs, so good value. Highly recommended.
Really comfortable left and right buttons right under where my fingers naturally lay. I bought the wired version for the office as I already had a wireless one I carry with me for site visits.