Personally I would not recommend a melodeon for a beginner to accompany singing. Firstly (as mentioned above) the limited keys that one melodeon can play in means carrying multiple melodeons around which is expensive and a nuisance. Secondly, by the nature of how a melodeon works the sound is very bouncy (due to the constant changing in bellows direction) which is why it is great for dance music. It is possible to play smoothly but this requires skills such as playing across the rows and ditching the oompah bass in favour of a mixture of single notes, chords and gaps. As indicated, a good english concertina probably best (but expensive) as you can play in any key and it is subtle. Accordions are cheaper and also play in any key but you will have to fight against their natural volume (and size).

The advantage of a free reed instrument is that it requires no skill to form a note. You press a button and hey presto the note comes out. Most other instruments require some degree of skill in bowing, fingering, breathing or mouth shape to produce a note which makes the learning curve much steeper. However, a guitar, bouzouki or mandola will probably in the long term give a better accompaniment to a song. Yer pays yer money and yer takes yer choice......

Richard Ashe