The feature that sets HEXACO apart from the Big Five is its first letter: Honesty-Humility. The Big Five has no clean home for this cluster of tendencies, so the variation it captures tends to slip through the cracks of a five-factor description. HEXACO pulls it out into a dimension of its own, gathering together sincerity, fairness, modesty, and a relative lack of greed.
What does this factor actually track? At the high end, an unwillingness to exploit others even when exploitation would pay, a discomfort with flattery and manipulation, and a genuine indifference to luxury and rank. At the low end, a readiness to bend rules for personal benefit, to charm or scheme toward a goal, and to feel that money, status, and special treatment are worth pursuing and deserving. Because it speaks directly to fairness, materialism, and rule-following, this is the dimension that makes the model especially useful for thinking about integrity, ethics, and cooperation.
Adding the sixth factor also nudged two of the familiar dimensions into slightly different shapes. Emotionality in HEXACO takes in empathy and emotional attachment, which gives it a warmer, more relational character than the 'neuroticism' it loosely corresponds to. And the tendency toward anger, which other models file under emotional instability, here falls under low Agreeableness instead, since losing one's temper is treated as a feature of how you handle other people rather than of how anxious you are.
There is a further point in the model's favour. That six-factor structure did not turn up in just one language and get exported everywhere else. It emerged independently from lexical research across many languages, which suggests the dimensions are not an artefact of one culture's vocabulary. That cross-cultural grounding is part of why the framework has held up.