Back in my Leica days I had one of those M4-2 motors (on an M4-2 and later an M4-P) and I didn't really think it was all that bad. Okay, I was a newspaper shooter in those days, so I suppose I was in the target market. But it actually was fairly useful.
Too tall, yes (although the height actually came in handy when I was using the camera on a monopod for theater shots; in this scenario, the motor also served as a "quick-release baseplate" for loading.) And yes, it did occasionally rip the sprocket holes when you'd hit the end of a roll of film, and yes, when I first got it I had to send my camera body back to Rockleigh three times for them to adjust it to work with the motor.
But once it was done, it wasn't so bad. It was rather quiet by motorized-camera standards, and once you got the touch down you could either shoot single frames or continuously just by how you pressed the shutter button.
There really wasn't much else they could have done, since the all-mechanical M4-2 and -P didn't include any electrical switches that could have been used to control a motor. The solution they came up with was rather kludgy: the motor rested in a spring-loaded cradle, and when it hit the end of the film advance stroke the motor torque would twist the cradle against spring tension. When it twisted enough, it would open a switch that turned off the power to the motor. The next time you released the shutter, the wind gears would be unlocked, releasing the tension on the cradle and letting it twist back the other direction enough to close the switch again, starting up the motor and banging forward another frame.
Considering all this monkey business going on inside, it was somewhat amazing that it worked at all -- let alone working rather smoothly and quietly, and at least semi-reliably.
The later M motors seem much better on all counts, and if I ever got back into Leica Ms I'd probably want one. There are times when it really helps to be able to track the subject without having to let your advance thumb disturb your shutter finger.