You don't take your hand off the keyboard for cursor movement on Datahands either but yes, having two embedded trackballs is pretty sweet.
Aside...
Datahand moved RSI pain from my wrist to my knuckles. These keyboards don't magically prevent all RSI, which is ... only obvious if you actually think on it, which i didn't back then.
I wouldn't even compare mouse keys to what is done on Svalboard.
I know I personally found mouse keys unusable for day to day use, and another local DH users thought much the same, we had other pointers we used. (I used a fingerworks trackpad back when, clamped onto the side of the laplander, the other guy used a mouse, if I remember right.)
I used a combination of left- and right-handed vertical mice, and swapped between them depending on which hand was more painful at the time.
The amount of time wasted moving my hand from one keyboard-half or the other to the mouse and back was very substantial, and it meant compromising on a comfortable position of both.
You really just never take your hands off the keyboard, everything is in nice close range, etc. :)