They seem pretty much the same to me except for number of keys. Below are the specs from Yamaha. In my reviews and comments I have expressed a preference for 32 key melodicas because they’re easier for me to hold in my hand and easier for me to play. But I regard myself as a hobbyist rather than a musician, and these are just personal preferences. I recommended the P37 to my friend who is a professional musician (pianist), and it has worked out well for him. He started out with my P32. He says the P32 “cuts” a little better, but I’m sure he’s using those extra keys, and the P37 and P32 sound the same to me. I wouldn’t worry about the weight difference; the P37 isn’t that much heavier than the P32. Depth and height are the two dimensions that I would consider, in relation to the size of my hand.