To answer your second question, I have found that the melodicas I play (out-of-production Hohner Piano 26/27/32) are no where near as stable as other brands of melodicas in terms of tuning. If your put AP Tuner (a free tuning software program) on your computer, you can see how your melodica reacts to changes in blowing pressure. My Hohners take a dive bomb as blowing pressure increases, dropping somewhere around 20 to 40 cents with even moderate blowing pressure (which still does not sound much like a bent note, but either sounds cool, interesting, or bad depending upon your perspective, what type of music you are playing, and the instrumentation you are playing with). I don’t intentionally tune off key, however, I did just recently have Hohner service tune one of my melodicas to A = 445. I have not experimented much with the results yet, but I think I like it at first blush for playing straight. (When the pitch dive bombs, I am still in tune with the other musicians.)
I can say that I love to bend notes and I could write a book about it. I will respond with some note bending information in your post where you ask about bending notes.