Pros
GKI is a great organization for people who want to work hard, have a diverse porfolio, experience opportunities for growth, and make a difference. It launched me on my career, and gave me opportunities I never would have gotten elsewhere: for travel, program design, program management, business development, and monitoring and evaluation. If you are willing to stretch yourself, GKI can be a great place to grow.
Cons
My sense is that this has changed since I was there, but pay and benefits were a bit below what its larger competitors often offered (as is often the case for young non-profits). It faced some of the other challenges small teams face: funding feast or famine, a staff with more energy than experience (I would include myself in that group), a somewhat informal HR and benefits system (by the way - each of these things improved while I was there, and have improved more since I left). This is not a con, but for some people it might be: there was a lot of work, and team members were expected to step up - and were rewarded for doing so. This wasn't an organization where someone could just punch the clock and wait for 5 PM. But that was attractive to me, as it was to most other team members.