I'll just respond with what i said in another thread:

Quote Originally Posted by Tenhou View Post
Avengers are among the least used classes on DMM, and for good reasons. Their gimmick requires them to go low on health and if you need to go low to deal damage you're pretty screwed and can be replaced by most things. One of the few avengers that actually could be useful is Uridem, the sapphire, since her skill gives her immortality much like Karma. However, the class as a whole is not too impressive.

If you don't have Rowanna there's about 3 reasons you might possibly want to get her:
1. If you don't have any stun immunity units she is one once AW'd
2. You like her looks and want her in your bedchambers
3. You want to collect all the things