However, and contrarily to what
has been stated above by our UK friends, here in France people have
generally sold all their ASK13 to buy replacement ASK21 or Twin Astirs
(at least those who were rich enough).

Well, not generally - A number of large and "rich" french clubs are keeping
their K13's and btw their market value is not decreasing.
K13s are much cheaper to purchase but do require skilled staff for
maintenance, so the large clubs tend to keep their K13s while small club
tend to move to plastic.

Having been trainee and trainer on both K13 and Twin - IMHO the K13 is much
more demonstrative and forgiving for instruction and first solo flights.
However a Twin would be more versatile for XC purposes

Jean