I myself am a third wife - of four. And I am happy with my lifestyle, eventhough it does have its challenges I find it rewarding in terms of self growth, relationship with hubby, freedom, the ability to build a career while having a great husband..
The jealousy thing pops up sometimes, but I am sure its less than if I would be in monogamy. There is nothing to protect now, while in monogamy you are alone trying to keep your husband's attention. I know my husband doesn't even look at other women anymore since he needs all his focus and energy for us.. :)