I have used Damsels to cycle my tank as well but they all lives forever and were healthy as ca be. The yellow-tail blue damsels are SUPPOSED to be the least aggresive, however, my yellow-tail blue damselfish was the meanest, most aggressive fish I have ever cared for, saltwater or freshwater. She had a nickname that isn't appropriate for this forum, but use your imagination.
Other than that one, I really like damsels actually, I like their color, their body shapes, and their quick speed. I unfortunately added a snowflake eel to my tank before I switched to reed and he took care of every damsel in the middle of the night. I had the yellowtail, a black damsel with yellow on the inside of his tailfin, and a couple brown/tan striped ones. I have never had any problem with the other damsels being remotely aggressive, maybe territorial to their "spot" but thats all. Go for it