Yep... done it. It works.. pretty sweet. I'm still trying top navigate that way since I was raised on capture Ones software and we use it at work. But yes... if you have the money, spring for it.
Nope, the computer only sees what the camera shot.
Why would that be handy if the computer saw it first? A lot of cameras have Live View, which is like what the point & shoot cameras have. But I don't ever use it except when I'm holding the camera above my head.