+1 for the Evoluent vertical mouse.
I first bought an Evoluent mouse in 2007 (at the time their newest mouse was version 3). I used that mouse exclusively until 2014 when I decided to upgrade to their newer version 4 mouse. In those first seven years I played 600 hours Modern Warfare 2, 300 hours of Team Fortress 2, and hundreds more in other games and typical desktop activities.
I had no issues using the mouse for desktop purposes but I did experience a learning curve adapting to FPSs. The pixel-perfect precision required by shooters can be difficult to achieve when your hand isn't flat on the desk. Games with a mouse cursor interface like RTS or adventure games are equally as easy to adapt to as regular desktop-ing. I recently replayed Delta Force and, for the first time in eight years, opted to use a regular mouse just because aiming in low resolution was becoming a hassle.
There are buttons for each finger provided you rest your middle finger over the wheel and ring finger over the right-click button. There are also two buttons for your thumb. The fourth edition unfortunately remaps some of the buttons to my distaste. This is something I've rectified using software (X-Mouse) and hope future versions of the mouse do not continue.
I hope to get another seven years out of this mouse before considering a new one.
