Sword Leapers are units unique to the nations of Southeastern China - Chu and Yue - and are in essence, an elite, dual-wielding sword unit. Although slower than normal Bronze Swordsmen, they have a powerful double-speed attack which makes them highly proficient weapon users, but even then, using them in mainline duty is not what Sword Leapers are for, given their heavy ramp cost.
Rather, Sword Leapers are better used like the Chivalric Orders of Chronicles to escort and inspire units, given their ability to boost attack of nearby friendly units. Remember, however, that Bronze Dawn is set in the Bronze Age, not the Middle Ages, so armour is rare and it is so too for Sword Leapers — no armour means almost no defence against massed skirmish elements. Sword Leapers are thus best used to inspire nearby infantry, but should not be too far from the influence of an Officer whenever possible.