Pros
There is a huge variety of work available. On a given day, you may work with economists, political scientists, sociologists, and defense analysts. The office is quite nice, and there are lots of resources to do good research. For policy the pay is OK, but much of the work can be similar to work done by (and compensated by) the private sector. The work is extremely flexible: staff at all levels are given flexibility to work from home and work flexible hours.
Cons
There are limited opportunities for formal professional development or growth. Most junior staff are too busy over-loading with project work to take time to learn new skills. One of the big cons of the 'internal labor market' is that project leaders will only bring staff onto projects who already are experienced in the methodologies being used. This means it's hard to 'learn by doing' because you are generally only invited to do things that you've done before.