Their feet sizes are all over the place- I have had 4 pairs of Duo over the years.
I am currently wearing Oristano in a 37 despite always taking a 38, and they almost fit my DD who is a 39/40! all other reviews say the foot is big in this style.
Others though fit more normally, including Kirov and Ravenna.
as a rule, I'd say that their pointy toe styles are big and their other styles are what you'd expect.