Honorable is a very good defensive trait. Most tanks can use this in combination with Energetic to become VERY tanky. In almost all instances I would use Energetic BEFORE Honorable, with the exception being teams with strong healing. When enough Healing is taking place, Honorable will gain more value.
Assuming fixed damage (no abilities that scale off of max hp), if you have 770 health it would take 1000 damage to kill you, which maths out to a 29.87% increase in effective hp. Which also means that any fixed heals you receive (not heals that heal for a percentage of your max hp) are essentially 29.87% more effective