Pros
RAND in Santa Monica is an unbeatable location and working in Santa Monica is fantastic for morale and general well-being. Whenever you're frustrated or need a break, you can go down to the bike room/surfboard locker and head out to the ocean. As long as you get work done and show up for meetings, timing of your work is pretty flexible, though that means lots of people tend to work late into the night. It's a very flat organization with little hierarchy. Pretty good benefits.
Cons
Internal job market is fairly exhausting for introverts - you have to network constantly to fill up your hours with project time. Even if you are 60 years old and the top of your field, your time will be spent writing grant proposals and drumming up business. For young researchers, there is little support, and you may have to resort to taking work outside of your areas of interest (the FFRDCs always have plenty of money and work to go around, compared to some of the other units that have smaller pools of funding).