I don't use an ergonomic mouse. I am using my keyboard probably ~20x more than my mouse, so it just doesn't seem that important. Mostly I am using my mouse to scroll around and navigate webpages, but when coding it's mostly Vim, tabbing between windows, typing commands in the terminal, etc...
I'm pretty much switching between stuff using keyboard, and mouse is mostly for "fine" scrolling, selection of bookmarks, and links, in most cases just page up/page down