Pros
IAVA is not only a cutting edge veterans organization, it is a cutting edge nonprofit. They play at the edges of what's possible (and sometimes what's popular) because the collective sense of urgency couldn't be greater. They impact the lives of America's newest veterans on the individual level, through their direct support services, and also the entire population of veterans, through their advocacy in Washington. That makes it an exciting, fulfilling, and fun place to work. Some of my proudest work has been at IAVA, fighting the good fight, because I can point to the veterans whose lives we profoundly changed for the better. When others said "slow down, be cautious," we went faster and got it done (most of the time). And some of my closest friendships were built in the IAVA offices - they hire great people to do hard, but worthwhile things. Those bonds were forged in the work and nurtured over a beer or three and the occasional Nerf Gun Battle.
Cons
IAVA plays a watch-dog role and ALWAYS speaks truth to power, if you need to be always liked that can be hard. Also, it's fast paced and everyone is expected to execute at the highest level. That can be stressful if you're not executing at that level.