On a piano, you use the bottom and top octaves about 0.1 percent of the time (except for Jerry Lee Lewis). You could chop the bottom and top octaves off and play 99.9 percent of all music written for piano.
So it is with the melodica. The very highest and lowest notes on 37- and 44-note melodicas are difficult to play gracefully and are almost never used in my experience and observation. You may have a need for them. If so, you should get them. But if you do not have a real need for these outliers, I would agree with Alan that 32 notes is enough. On a 32-note melodica, all the notes are useful and the instrument is easier to handle.
In my playing style, my favorites are 26- and 27-note melodicas. I rarely feel that I need more notes. Sometimes I play a 32-note instrument for added range, but even it seems cumbersome to me.
That is one man’s opinion and does not include title, tax, and registration fees.
If you need all the notes, by all means you should get them. There is something to be said for holding a big, beautiful, substantial, and long instrument.
Lowboy