I don’t know the meaning of those designations.
I also don’t understand the distinctions made between professional, intermediate, and beginner. The M-37 is heavier, bulkier, and has a few more keys than the A-34 and M-32. It also has a fancier appearance. But all three look much more like real instruments than most other melodicas do. Quality of construction is comparable and very good. I gave the M-37 four stars in my review, but now comparing them I think it probably deserves five. Here are some sound samples for comparison. You can judge for yourself how much difference there is between them.