I've never had the joy of playing them, but I found that the LoTRings "Warriors of Harad" box was pretty darn good. Well crafted, not too tiny, and 24 guys for $27 US.
As for balance, they look about par with the Witch Hunters or Merc warband. When in doubt, use common sense, and ask the other members of your group:
For example: As is their special rules, "A Muzil tribe may include up to 2 Scholars." While not included in the rules, it would make sense that one of the Scholars would replace one of the Askar. And while not stated in the rules at ALL, the terms of sportsmanship would suggest that you couldn't have more than one caster in the group (so you can't have two occult scholars, or an occult and a theology.)
When in doubt, ask YOUR group... they are the guys who are going to have to play against it.
Also, if you're playing the Relics setting, then you probably have nothing to worry about. I've generally found that most warbands are balanced WITHIN a setting... it's when you take them OUT that the balance difference starts to show. (For example, the Fallen... they can be MEAN!)