Slitherine

52 pts, Superior, Protected, 50% Bow, Light Spear+Sword Cav. 8 pts more than Noble Cav which don't have bow, and 4 pts less than Fierce Nomad Horse Archers, which have full bow, but no light spear.

How exactly do you use them effectively? Unlike other armies with hybrid cavalry, these would be the main source of non-light firepower for the Rhoxolani army (unless you add Skythian allies)

I mostly use them as a sort of second or third wave, after the light cavalry and dedicated horse archers have used most of their ammunition the light spear cavalry strike at disordered units or pin intact units in place for dedicated horse archers to flank. The bows are useful for pushing units just over the edge into disordered or fragmented with minimal risk to your own fragile units, but I don’t treat them as the main factor as the army has plenty of horse archers already.