I used an M-3 (with a Leslie 147RV) for quite a while...it was the usual spinet style with the shorter pedal board, drawbars for the two 44 note staggered manuals, and no presets whatsoever. It was, however a great little organ with the same sound as it's bigger brother, the B-3 and a really superb chorus/vibrato.
It has all the essentials for organ work, including harmonic percussion, although the shorter keyboards and one octave pedal board were sometimes a disadvantage. Still, the keyboards were beautifully made and very responsive.
It was also considerably lighter than a B-3.
One of it's close kin, the M-102, was used by Matthew Fisher (Procul Harum) to record the enduring rock classic, A Whiter Shade Of Pale, so these instruments did have that legendary Hammond sound.
Ian
For sure, Ian. That old M102 I had was built like a tank.
Originally, I had an L102 and, as nice a condition it was in, I traded it straight across for the M.
How it came about was we were booked into this seafront pub in Southend and this banged up M102 was just sitting under a sheet at the back of the stage. So I asked the landlord if he'd be interested in a straight swap for my immaculate L102. He said yes, and We drove away with the M that night.
One trick I used to like with the M was having the 2nd percussion tab down and then just easing down on the 3rd tab. It would put a lovely 'scream' into the percussion.