What are the pros and cons of using them online? In 1v1 or team games. Doesn’t matter.
pro tip: Dont play japanese.
pros: good early game eco bonus, good MAA opening, some of the best late game Halbs in the game.
cons: average UU, no Bombard Cannon, weakish late game without a true mobility option other than Cav Archer. In a 200 pop scenario vs a stronger civ with more efficient units like say Berbers, they lose every time, but they also get to their ideal composition (Cav Archer + Halb or Arbalest + Halb) faster than these stronger late game civs.
Overall on Arabia they are middle-of-the-pack civ and on water maps/hybrid maps they are top 10, sometimes even top 5 (e.g. 4 Lakes). On Arena they are probably a bottom 10 civ and a no-go.
They are good vs. Goths and on water maps. Good towers. That’s about it.
Pro Tip: Open with Man At Arms
Pro Tip 2: Make use of Unique Techs in the late game
Pro Tip 3: You have CA and HC, Monks too, not only Arbs or Infantry.