Hi Ian,
Thanks for showing interest. The concertina belonged to my late father. I do not know how to play this instrument myself, so cannot comment on the benefits or difficulty level of a 40 key over a 30 key concertina. Maybe you could post this question elsewhere in the forum. I am also not sure if the reeds are steel or brass, but will try to find out. I am not really wanting to open the instrument to check. All I know is that it was manufactured in 1954, because I have checked the serial number against the production journals. Not sure if brass or steel was the preferred metal used for the flutes by Wheatstone during this era. How can I further assist you?