These tribal levy troops are basic spearmen. Though fierce in the charge, some may question their staying power in battle, and you should not expect them to last long against professional infantry.
Among the Thraikian tribes, the vast majority of men of military age are too poor to fight in the bands of well-equipped units. As farmers, herders, and general pastoralists, many of these Thraikes cannot afford more than a few pieces of military equipment. For that reason many of them carry simple wooden shields, a clutch of javelins with fire-hardened wooden tips, and a simple spear. While many of the warriors who perform service for their tribe are these farmers, herders, and fishermen, many of them are also accustomed to a form of warfare through their incessant, low intensity squabbles with neighboring tribes, or even through occasional raids on passing trading parties or local trading emporia. So while they lack good weaponry, or armor, they carry a ferocious disposition - they are Thraikes, after all. While they may carry their ferocity on to the battlefield, their lack of experience in much of anything larger than a skirmish over farmland may cause their ferocity to dissipate in the face of prolonged hand-to-hand combat with well-ordered, or even professional, soldiery. They are accustomed to short skirmishes and decisive charges, and so are best used in similar roles.
Cheap and numerous light infantry. They are alright for levy troops and they can be used to hold the line(although keep your general near them due to their low morale) but not against phalanx units or heavy infantry as they will be beaten.
They do however have a powerful charge so they may be used as an light assault unit to rattle and rout an enemy line.