Jinettes are the best missile Cavalry availible to any Western European faction. They are recruitable from turn 1, and still just as good (perhaps even better because of all the dismounted Knights appearing late) at turn 200. Their armour piercing ability and allround usefulness makes them special.

The Portuguese get most everything that the Spanish get, including the Spanish special unit - Conquistadors. The Portuguese lack the "Military Academy" and "Royal Military Academy" buildings leaving them without Tercio Pikemen and Gendarmes. Instead of these buildings they get Naval Academies which makes the Portuguese Navy not only better than the Spanish, but the best out of any faction.

The fact that the Portuguese and Spanish get similar units is due to the fact that the two Iberian nations had very similar tactics at the time. Historically, they were both extremely fond of Jinettes in the Reconquista.