what do you like about using a trackball? what makes for a good trackball?
The primary appeal of a trackball (for me) is space usage: a mouse occupies everywhere on a desk it could possibly move to and putting other stuff down shrinks its useful area. Trackballs are fixed in place and so you can pile as many microcontrollers or embroidery projects in front of you as you want without impinging on your mouse.
I also like that it's always in the same place. I usually keep it stuck right up in front of the numpad, so when I need to use the mouse it's right next to the keyboard and I don't have to worry about where on the desk it could be.
Trackballs used to be pretty popular with everyone because they were nicer than old ball mice. Nowadays as far as I can tell the main users are “people who got used to trackballs in the 90′s” and “audio/video engineers”, because AV techs usually have mixing decks or keyboards taking up a lot of their desks and it’s nice to have a small but versatile pointing device.
As far as what makes a good trackball, well, I've only used two for an extended period of time, but everyone has opinions. Personally I dislike the Thumb Trackballs like the ones Logitech sells
because the thumb isn't a particularly dextrous digit. I use "finger Trackballs" where the ball is available on the top, and so you can manipulate it with your whole hand. This means you can go down to fine finger movements, or go all the way up to swiping across the ball with your palm.
I find that using thumb trackballs is very strenuous after short periods of time, it requires a lot of precision and has no good lazy fallback, whereas the finger trackballs can be palmed about and are generally easier to work with. Your mileage may vary, but I like this.
This one in particular has some nice features. It has a scroll ring for scrolling, which is fancy (although only Kensington trackballs have it for patent reasons, boo, hiss, etc.), and a reasonable set of buttons: left, right, and middle click, plus forward and backward. I don’t use nav buttons, but I bound forward to function as a modifier. If I press the forward button and move the trackball, it scrolls around freely in 2D. This is the objectively best way to scroll in my opinion and weirdly as far as I can tell it’s only natively implemented in Linux’s xinput mouse driver. There’s no option for it in the Windows trackball software.
I also like having a few buttons I can press without having to fully grip the mouse. When I’m just playing a Visual Novel or reading an ebook or some other interface where I click to progress something, it’s nice to just whack a side of the mouse. My old trackball was pretty good for this, and of course the creme de la creme of trackballs, like the Elecom Huge or Kensington Expert, have plenty of upwards-facing buttons.
They’re not for everyone, but if you don’t like having to reach for your mouse, have limited desk space, or you feel like using the mouse for extended periods of time causes you discomfort, you may want to consider it.