Yep. I'll just add a few thing to that too.

Arcani cannot hide while moving but can hide anywhere on the battlefield as long as, as SMZ stated, they are not in direct range or line of sight of the enemy.

As for using Arcani they are brilliant for a sneak attack on the enemy General if he's positined at the rear of the enemy army or something. Also Arcani are good for flanking an enemy unit and of course also as SMZ stated for clearing and taking walls.

Thanks