I just completed a very satisfying Celtic campaign (my first successful!), all thanks to the Hounds. However, I did almost lose Ravanna to the Huns because of them.
One word of advice: Do NOT use them for city wall defense. They will go berserk, and try to find their next target (on the ground), and will go outside the city walls to meet their foes, and will ultimately die. Worst case scenario is that they will give the enemy good time to move up into the siege tower and take your walls, or (even worse) walk through your open gates.