This full-featured predecessor of the MM-3 has the same features (many
memories, Beacon Mode, Morse Trainer), but with an important
difference -- it's easy to add a diode in series with one of the AUX
jacks so that a computer can key the rig in parallel with the MM-1
(like Elecraft did with the K2). I've done that mod,and used a pair
of these keyers in my rather primative SO2R station until I bought K3s
and added the YCCC SO2R box.
I have two of these very nice keyers for sale, both in very good
shape. Asking $105 for each, shipped to US ham.