Ratings are based on what was out there during its time (1971-74). This was the original Motor Drive for the F-1, it is often referred to incorrectly as the Motor Drive MD, probably because everything that went with it had MD at the end of its name, i.e. Battery Checker MD, Remote Switch MD, etc. I have 2 of these, one is used - lightly, and the other is essentially new in the box with everything including the hard to find Battery Case D!. This was Canon's first attempt at a motor drive and it while it appealed to the scientific user, with its built in intervalometer, it was not compact even for its time, and in its original rendition, the battery case was a separate corded affair, not all that useful for action / sports photography. The speed at 3FPS was not that great either. The Battery Case D came out shortly after and allowed the power source to be directly attached, but it didn't help the overall bulkiness of the whole affair. On the plus side, it was very rugged, and flexible. Further, it could mount to ANY F-1, you didn't have to send the body for custom modifications like nikon F users had to if they wanted to use the almost equally bulky original motor drive for that camera. The external battery case could also supply power to the Booster T or Servo EE Finder this saving a small amount of bulk, however, the arrival of the Motor Drive MF relegated the Motor Drive Unit to the scientific community and those who really liked to load themselves up with gear!