I used to always use mouthpieces but after seeing some videos of “famous” players using the tube I use it almost exclusively. One thing I do different is I don’t use the mouthpiece on the end of the tube. My first melodica didn’t have a mouthpiece on the tube end and I feel like I am getting more air into the instrument.
I’m a visual player so I like being able to have full view of the keyboard, feel free to hold the instrument in different positions if my hand is tired and I don’t feel like I’m going to pry my teeth loose.
I’ve read where people have said they thought the melodica sounds better with the mouthpiece or blowing directly into it? However I think part of this could be due to proximity of the instrument to your ears? I’ve tried playing with the mouthpiece then playing with the tube but holding the melodica the same distance from my mouth and I can’t hear a difference.