Similar devices are not unknown among large format photographers. The new idea of the QuickDisc is the round shape. With a rectangular device, you have to care that it is perpendicular to the optical axis, or it will be foreshortened and therefore give an incorrect reading. With the circular Quick Disc you do not have to worry about the orientation, you just have to measure the largest diameter to get an accurate reading. You can print a copy of the QuickDisc on you own printer after downloading the QuickDisc file.
Basics When photographing small objects the increased lens to film decreases the effective f-stop.
But only few large format cameras are equipped with such sophisticated metering systems. In studio work exposure is often determined by trial and error with instant image film. If budget or weight is a concern, you have to correct the reading of a hand held exposure meter with a compensation value. To get a correct exposure, the photographer has to increase either the exposure time or open the aperture accordingly.