There's also https://mousefix.org which has the extra bonus in that it tries to solve the smooth scrolling problem that can occur when using a mouse on a mac.

I just noticed that Steermouse has high CPU usage 5% if you continuously move your mouse cursor. I have a brand new MacBook Pro. It's using more CPU Time than Mail, Finder, Terminal.

Steermouse the easiest to use with most functionality so far compared to Sensible Side Buttons, USB Overdrive, ControllerMate. I tried out Steermouse for past couple of weeks. Just paid for it yesterday... but noticed the CPU usage today.