From their website:
These models represent Western Islamic (Bedouin and other Arab) forces from the late Umayyad Caliphate until the Crusades, and in fact many can be used for quite a bit later than that. The Arabs seem to have adopted the turban after the conquests in the east exposed them to this headgear, and these models include some with turbans, while others have the traditional egg hat (which can also be painted as a leather or metal helmet).
These models are suitable for later Umayyad, Abbasid, Hamdanid and other Bedouin Dynasties, Fatimids, Arab Indian, and other armies which used more traditionally dressed Arab troops from around the 8th century on. The Eastern Arab Cavalry is also suitable for Kurds.