Kahliel’s Tribesman is the cheapest harad ally (tied cheapest with the Southron Refugee). Usually, when there's a really cheap ally people assume that it's not great. Not the case with this ally. Decent stats, but it's the ability that shines. By exhausting the tribesman you get to boost another Harad character's stats by 1. For example, you can make Firyal 6, or Yazan 6, or Jubayr 6 with three tribesman.
Who they work well with:
My opinion: 6/10