I wear Sidis b/c they fit my low-volume foot and have a squarer toe box, which I require. They also last a long time, in my experience.

Sidi's own website says that the half sizes are not longer, but higher-volume than the full sizes. That is, a 38.5 is no longer than a 38, but does have a higher volume to accomodate a *meatier* foot.