Guys,a couple of short comments before I am off for some days...

Alan,
Yes! Children can teach us a lot if we just listen and learn...

GuestLDT,
Handbag was a fine example! - I can't imagine carrying my wife's.And what you say confirms the declaration on strenous pumping.

GuestBlackBelt,
You said:"A heavier instrument means more inertia to overcome when reversing direction"

NOPE! - not a bit! This is one of the common misunderstandings.You are
constantly working to overcome the pressure gradient.Both on push and pull.As soon as your own applied force ceases, air flow and sound stops and the ends don't move anywhere from any "inertia" - unless you twist and turn or swing the instrument about, but that is not needed and you need no mathematics for it...

I fully agree about possible problems with button width and profile.
This is a constant riddle to me.All other keyboard devices - musical instruments,phones,computer keyboards,calculators etc have a lot more
comfortable buttons than British tradition concertinas.10-15mm wide flat or concave(!) profile is expectedly the ideal situation unless you want to press more than one button with the same finger when a convex profile may be preferrable.
I use flat 6mm buttons on Englishes.I have changed to up to 10mm ones on anglos.

ConcertinaChap,
Ca 1000g for the Morse?1500g for the Jeffries? Never mind - it really should not matter even when standing.It may be a matter of habit rather. Try using a shoulder-strap just for curiosity (and let the instrument hang in a rather low position )to get used to not thinking about the weight.You don't bother about it when sitting...:-)

Goran