I have one, and I tend not to use it much, but don't discount such things until you've tried them.
I find the calculators on the Sinar cameras very useful, so I thought I'd get the Rodenstock calculator so I could use the same features on any view camera, but since it's not so nicely integrated into the camera, and many shots that I take are pretty simple anyway in terms of figuring out the movements required, I don't use it that often. If you shoot a lot of tabletop and still life, you might use it more.
A good companion to the calculator is a device like the Suunto Tandem clinometer-compass, which will allow you to measure tilt and swing angles on both standards on any camera (well, any camera that doesn't have any strong magnetic parts), whether it has scales or not, and the angle of the plane of focus.
$29 is a good price, as I recall.