Yes, Varangians are great in SP, but be careful im MP with them. V2 AUM can face them off for 100 florins less.

Byzantine Cavalry is my favourite unit I guess, much cheaper than Boyars and only -2 in charge and def.
Don't be afraid to commit them to melee, they will handle all but heavy cav and spears.
Lets see what you get compared to the Pronoiai Allagion:
You get the same defense, -1 to attack, -4 to Morale (but it still good at 4), -4 to Charge (they are Horse Archers, this is not their game), -1 to Armour the same as Feudal Knights (not counting the shield) but most importantly you get bows and 50 florins in lower price.

Pronoiai Allagion is basically the same unit as Feudal Knights. It has +1 to Armour (but not def) but lacks 2 in Charge having 'only' 6 as opposed to the Feudal Knights 8.
But I don't know... It seems they don't tire as fast as the Feudals though...

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BTW, Danish Crusades are true to history.

You may not care about war, but war cares about you!