Just to give other ideas: On my 16-button, I have Volume up and down, Ctrl (+click to open in new tab) and Win(acts like altdrag on awesomewm), Mouse4 and 5, ctrl+tab and ctrl+shift+tab(next/previous tab), Ctrl+t and ctrl+w(new tab and close tab), win+tab and win+shift+tab(next/previous window), and win+left/right/up/down which I’m to lazy to remap to something more useful now that I’m not on windows anymore. The 5 extra buttons on top are rapid click, doing 40 clicks per second while held down, and stock dpi up/down, lighting mode and profiles switches that I never use.
It was mostly empty and unused for years, but when it finally broke It felt like I had a hand chopped off, so I pretty much had no choice but to buy the same one again, even though it is heavy as fuck and the cable is stiff like rebar.