Long term, what I really want in a split mechanical keyboard: trackballs on both sides, near the spacebar, with intuitive mouse triggers built in. Maybe even a trackpad on one side, trackball on the other. That would be slick. One input device.
The wide split is great for shoulders and the shortcut panel helps with cutting down on common multi-key movements (copy, paste, etc).
The Pro steps up from the other Freestyles with mechanical keys and programmability. I'm using the programmability to remap some of the modifier keys for comfort. Combined with the panel of common shortcuts, it's much easier on my hands.
A bonus of having a programmable keyboard is that you don't need to rebind keys in the OS, something that's not always possible to do in corporate environments.
One thing I really love about the Freestyle is that, with the stands and hand rests, it actually sits very nicely in the lap, for when you want to sit in the living room with the laptop on a coffee table.