In my previous job I tested Logitech's Marble Trackball mouse and fell in love with it in no time. I decided to buy a similar trackball for home use with more buttons and ordered the GameBall.
My PC is already a "RGB hell" so GameBall's changing light color works as a natural extension aesthetically. The trackball requires no additional software to be installed, and any button settings can be adjusted for one's liking. There's a dedicated button for changing the DPI. The DPI button is really useful for tasks where I need to be more accurate, such as music editing and mixing.
Well, it's a gaming mouse, how it works for gaming? I don't really play FPS games and I mostly use a gamepad, but I'd say that GameBall could be a fitting option. Someone who plays FPS games actively with trackballs could have a more thorough opinion regarding this.
Around the ball are two touchpads that function as scroll wheels. That allows for horizontal and vertical scrolling when zooming large images for example, so that's what I find useful.
During the first weeks of use I had to get my hand to accommodate to the mouse, which made daily use somewhat awkward. After that however things go really smoothly, there's no turning back from trackballs for me!