amazing, discovering new input devices “everyday”.
the difference between the free2 and pro2 is that the free2 has a open roller bar, and detacheable wrist pad, and more precision (dpi). It's also about $40 more expensive.
With this, you don't have to “move hand off keyboard” anymore, but am not sure it's better than mouse.
Depending on how much you type, moving hand off keyboard may be a good thing, because it provides your hand muscles a break. Also, we programers often like to say we type all day, but you need to actually log your keys to know how much you really type. For average programers, a whole day's typing is probably less than 20 minutes typing when done continuously. See What's the Most Efficient Keyboard Layout? Dvorak vs Colemak? and Bad Advices from Programers about Typing ＆ Keyboard (RSI).
thx to to1ne