I have a few of my characters as merc heroes. Also think of mercs as "mirror images" when they're created. They will retain the same looks (including costumes, or naked), and they won't disappear if the original character is deleted. I created a few temporary PvP characters as well. For example, I created a few chars named Undead Sherlock, and Undead Watson. Those character names are still available as I only used them temporary for my mercs and then deleted the characters.
I would say mercs makes well for show casing your elite armors. (If you ever party with real people)