Unlike many others for sale, this iKorg 01/WFD has new backlight display. Floppy also works.

If you're looking fo an M1, this does all the M1 does and much more

from Wikipedia:

The 01/W is also known for its "warmth". It has been suggested[citation needed] the 01/W sounded richer than the Korg synths that came afterward. The two most probable reasons for that are:

The 01/W's samples were recorded at 16 bit 32 kHz. Subsequent Korg synths had their samples recorded at 16 bit 44.1 kHz[citation needed]. The sample rate of 32 kHz limited the frequencies possible in any sample to below 16 kHz, instead of the 22.05 kHz of later synths by Korg.

More ROM memory was allocated to each sample than the synths following afterward (As an example, the 01/W used 6 MB of ROM to fit 254 compressed samples. The Korg X3 also used 6 MB to fit 334 compressed samples in its ROM)

The fact that the 01/W's samples were recorded at a slightly lower sampling rate, therefore reducing sample size, plus the advantage of having more ROM memory meant that longer samples could be stored, possibly adding more realism to sustained sounds and so forth. The 32 kHz frequency might give the illusion of a more acoustic instrument, because it might be perceived as reducing the amount of high frequencies, which tend to be attenuated in physical/analogue instruments when compared to digital ones