Quick question, as I've never actually, physically seen one of those. Is it like any other film holder, like a Polaroid film holder for example, in that you can view and focus with the ground glass, then slip in the rollfilm holder and take the picture. If so, this would allow using some of the camera's movements... Or, do you install it on the camera and then you have to rely on the camera's viewfinder and rangefinder?

To use any of the Graflex Graphic roll holders, your camera must be equipped with a Graflok back, which has a removable focus panel and sliding bars that hold the roll holder onto the camera. With that setup, you can work two ways, leave the roll holder on the camera and focus with the rangefinder, or use the focus panel and ground glass to focus and switch back and forth. (focus, rmove the GG panel, lock on roll holder, etc.
The Graflex Graphic roll holders do not fit cameras with a standard spring back.

The rollfilm adapters made by Graflex for the "Graphic" press cameras really are designed for use with the "Graflok" back. They are much too thick to slide under the groundglass of a spring-loaded "Graphic" back.

I worked for years with a "Century Graphic" with the "23" rollfilm adapter, and never found replacing the "Graflok" focusing panel with the rollholder to be inconvenient. Some contributors to this board disagree.

As you suppose, the rollfilm adapters are very well suited to use with the rangefinder.

Thank you. Now I understand.

With a Graflok back, the ground glass back does remove readily to allow easy installation of the roll back... but that's impractical if you're hand-holding or using a flimsy tripod.