Not all the Jatu riders are savage raiders. A number of them have shown to have more of an affinity towards the "civilized" world. Why put so much effort into raiding their villages and caravans and be branded as "bandits" when they can get all they want by selling their services to the right person and for the right price? This way they still get to fight and raid but without having to live off from one day to another, constantly being hunted by the law and those pesky meddling adventuring companies or the would-be prophesised king.
The Jatu Mercenary Riders are pure melee cavalry troops. Their melee weapon can be either their signature sabers or honor lances. They have gained a well deserved reputation for being terrifying raiders, often being able to run down any foot soldiers and fell even mounted knights with but a single strike (in this case, usually with a couched lance).
They ride on unarmoured steppe horses, which have decent speed and great maneuverability, but no armour (a few good blows will easily dehorse them, leaving them vulnerable to other passing horsemen and with no advantage against foot soldiers). They wield their weapons with decent skill and they have good stats, but high tier troops will easily overpower them due to their superior equipment. They can rise up to expectations only when they have the advantage of numbers, as they individually don't show outstanding combat prowess. Their upkeep isn't as low as you might expect, they can actually be quite pricy for what they are actually capable of (depends on their numbers). You should try to hire them only if you feel confident of your purse and in your skill to command them.
They should be treated as light cavalry, and they best serve to flank the enemy and to run down any fleeing troops. When facing them (only when they fight as a mercenary company for an opposing faction), they can be extremely deadly and irritating. Their lances may decimate unwary any unwary soldier, on foot or mounted, but once they are dehorsed, they shouldn't pose that much of a threat.
They can be encountered in taverns or as mercenary companies, either fighting for one of the major factions or willing to join your cause in exchange for a fee (through a heartbeat quest). You will also spot them in the tournament lists, being allowed to participate as they are no longer labeled "barbarians" and they show decent skill, capable of facing even Hero Adventurers with relative ease depending on their equipments.