I guess that leads to similar effects. The distance
between two adjacent megahexes is sqrt(7) = 2.65 times the
distance between adjacent hexes. The average distance between
two adjacent megasquares is 3 times the distance between
adjacent squares. Not too different.
I'd be tempted to say that diagonal moves cost 1.5 but
maybe that isn't essential.
A diagonally adjacent character is quite a lot further away
than an orthogonally adjacent one.
How did you handle facing? Maybe three front squares, a
square where you can attack with a one-handed weapon but not
use a shield, a square where you can use a shield but not a
weapon, two side hexes and a rear hex?
I think hexes are better than squares in natural
environments, but squares are better in artificial ones.