I have Motor M's on my M6 and M7.
The real test for me is 'Does the device improve my ability to capture in a photograph what I want'.
The Motor M has three Modes, O or OFF, I, which allows continuous picture taking at a slower rate and is designed to be as silent as possible and II, which allows continuous picture taking at a faster rate. There is no C or S.
The I Mode is very quiet to the extent that in practical terms, thre is not much difference between I and using the camera in the O Mode by manual winding. I never use Manual winding anymore, the Motor M is that quiet.
Being able to concentrate on framing and especially with the M7 in AUTO, leaves Focus as the only other factor needed to be done. Even with the SF24, the TTL exposure is transparent and again Focus and framing are the only requirements.
I even use my 128mm 2.8 RF on these cameras by installing the RF lens before the film and Motor.
I wouldn't be without them.-Dick