I agree for the most part, feeling the anger is a very important step to understanding where it comes from inside and the analogy of it being a guest is a great one. But (and this could just be the limitations of language so we may be saying the same thing) I disagree that expressing anger is always harmful.
I think the conventional idea about anger is that the only way to express it is to shout, yell or worse, physically assault somebody. To me that's just an unhealthy form of expression, that seems to come about due to fear or repression.
Imagine a friend punches you jokingly in the arm every time you see them and you find it uncomfortable. It's unhealthy to scream at them, sure, but IMO it's also unhealthy to just sit there and feel the anger mindfully while continuing to let them do it. The middle way is to tell them assertively to stop it. It doesn't have to be unkind - just like we wouldn't consider a cat unkind when it nips at you for invading its personal space for patting it too much. The cat is using the only expression it has to warn you about its boundaries, but most cats don't go off the rails and start tearing you apart because it was slighted.
Personally I never had a healthy example of anger growing up -- only dysfunctional examples -- so I believed that the conventional expression was the only way to express it. The conventional expression felt scary, so I avoided it at all costs. It took me years to realise that I was so afraid of the emotion and expression of anger that I was even using meditation and mindfulness to continue to repress it.
The more I began to express anger in these healthier ways, the less that heightened state of arousal comes up to the point where it's very rare that anger sticks around for more than a few moments now, and is far less intense in the body.