Using control keys and mouse buttons is exactly what made me switch to a spacemouse. I spent many years twirling around in 3D space the old fashioned way, and as such, my hands are left pretty sensitive to RSI-like fatigue/pain. Spacemouse is absolutely the answer to that.
For 2D CAD applications like your typical Autocad, I'm usually 99% keyboard input, shortcuts, macros, etc. Little mouse input other than clickpoints.
For most any 3D modeling, I use the spacemouse for all navigation and the standard mouse for command clicking. My left hand will bounce between the spacemouse and the keyboard as required. Numerical input would be the hand on the standard mouse going to the keyboard numpad. I would think having a Spacemouse with numpad built in would eliminate the right hand (strong hand / standard mouse, for me) going to the keybaord entirely, for me.
Yes one hand still has to hit the keyboard from time to time, typing notes, entering numbers, etc. It's honestly seamless and not intrusive to me. However, the tiring middle-mouse-click-and-drag for panning or orbitting is eliminated and the Spacemouse is worth its weight in gold for that alone. No more shift+left-click-and-drag or even worse, the dreaded MMB+RMB and drag... the endless middle scrollwheeling for zooms... what a chore.
I only wish I switched to the Spacemouse years ago, rather than waiting until about 1-2 years ago.
I can't compare it to the newer contender, the "SpaceControl" but the 3DConnexion is absolutely golden. It has a good weight to it, excellent 6dof input, and respectable button mapping that can set software-specific.