Pros
The easiest job you will probably ever have. Very few expectations from management. Total job security as long as the executive leadership likes you. A friendly culture and some of the nicest people around. Unlike most non-profits the company really does care about protecting its members and its mission. Cooperative, non-competitive environment where everyone truly tries to help each other. Great if all you value is having an easy job with stability.
Cons
Blatantly nepotistic with little regard for fairness. Job titles mean absolutely nothing. Meaningless title promotions with little actual pay increase are common. Very strange culture rooted around executive worship that you are expected to participate in. Yes-men are everywhere. Expect your position and responsibilities to be reshuffled regularly with no prior warning. If you are one of the few outside hires you are viewed differently from people that are hired based on connections. Not much upward mobility unless you share a surname with an employee in a senior position.