Well, first there is the precision of the fit when it is mounted on the Canham 5x7 metal camera - we're not talking about wood to plastic or wood to metal - it's a metal to metal fit. Then there is the manufacture and function of the automated back itself. If one is shooting 6x17 on 120 film, I suggest it is the best, most high-precision made rollfilm back out there. After each shot, you press the film advance button and the motor advances the film to the next frame. Here is the description from the KB Canham page for accuracy:
K. B. Canham is pleased to offer the first motorized 6x17 roll film back for use on any of the Canham 5x7 view cameras (other cameras can be used, but note that we have not personally try this roll film back on any other cameras, but have heard of other photographers that have been able to adapt the roll film back to other cameras). The back is manufactured from 6061 T6 aluminum. Each metal component is machined from solid aluminum blocks. No castings are used. This method of manufacturing assures that each part is made to the most demanding tolerances. The film plane, pressure plate, is flat to within 0.0005 inches (0.0127mm). The back operates on a 9 volt battery. The electronic film winder has built in memory. This permits the user to change batteries mid-roll without losing film position. A low battery warning is incorporated to let you know when it is time to change a battery. The warning lights blink early enough so that the film currently in the back can be completed before you change the battery. Approximately 20 rolls of film may be shot using just one battery.