These mobs are great experience around Level 14 - 16 in a two person group (monk, red mage), and we were able to kill 2 or 3 in a row without much trouble. Even cons were easy to take without any TP, and the tough con ones were pretty easily killed using TP and Fusion or Liquefaction Skill chains.
They do have some special abilities which can cause you some problems, though. If you see them use the "Beserk" ability, the amount of damage they do to you per hit is going to almost double. They also have a silence ability (called Stone Stare, I think).