I’m probably in the minority among the members but I only play with the tube.
I grew up playing organ not piano. I recommend the experience to any melodica player. The piano has almost no relation to playing the melodica. but I also played trombone throughout high school which gave me a feeling for wind instruments.
I think of the melodica as a small reed organ or harmonium.
When I first had a melodica I used the mouthpiece but years later when the videos became easily accessible on the internet I noticed many of the “top professional” players were using the tube. I thought if they aren’t embarrassed to play that way neither am I. It really freed me up to hold the instrument how I wanted. and not worry about whacking my teeth, I could take advantage of two-handed techniques and I was able to see the keyboard, very important since the keys are non-standard size.
As far as the instrument responding differently, I don’t think so. I think that notion is all in their head! :p Seriously the proximity of their head to the reeds. Holding the instrument up in the air near the ears sounds very different than placing it on a table or holding it in your hand away from your body.
I know that experience from plectrum string instruments. Fine guitars don’t sound well to the player the majority of the volume should be projecting from the front away from the player who is behind the amplifying box.
However, I have a simple experiment to find out if it’s true:
Play your melodica for a bit through the mouthpiece. Then plug in the hose and hold your melodica at the same angle and distance a mouthpiece would put it. See if you notice a difference in the sound or expressiveness or any other variable.
Alternatively you could record mouthpiece and hose playing being careful that the microphone is the same distance and angle wait a bit then see if the recordings sound different?
Or you could play for someone to see if they hear a difference.
One more thing I will add is I usually don’t use the mouthpieces on the end of the hoses. I usually pull those off and blow into the end of the tube. just a personal preference. I don’t think it alters the playing in any way.