It's good for more than A mixolydian tunes. Second position will give
you E dorian tunes (The Warlock, Johnny Wilmot's Fiddle, Drowsy Maggie)
while third position will give you natural minor with a full B minor
chord (Sleepy Maggie, Elmer Briand's Favourite, Da Rain Dancin', can't
think of others right at the moment).
I notice that they left the D side of the harp alone. If they'd flatten
the Draw 3 and 7 on that side, too, then you could have E natural minor
in third position and A dorian in second. There is a huge number of A
dorian tunes at least in Scottish tradition. (And you could play blues
by playing the I chord in first position on the A side, then the IV
chord in first position onthe D side.)
Hmmm . . .
One thing about nails is that you can put them in places where screws
won't go. They're pesky for repairs but have that advantage for
assembly.
Winslow