Thanks Anahata and Bob for your comments on my question about singing with the concertina. It sounds like I should get an English concertina since, at least at the beginning, I will probably want to do more songs than tunes.
I did have the impression the Anglos were limited to certain keys, but I wasn't sure how limited they were. Your descriptions help a lot. I find with singing that I'm sometimes most comfortable with a sharp or flat key (Eb seems to come up a lot with my voice) which would be difficult on some instruments. Although sometimes it works to just sing up or down a half step - not ideal but passable.
Bob, I did get to hear Danny Spooner last year. He performed at the 2003 Old Songs Festival here in New York State. I enjoyed him a lot, but I'm afraid I was listening in an overall sense, and didn't pick up the specific concertina style he was using. Perhaps I'll get to hear him again at some point.