Pros
Flexible work hours, small company so you get to know and spend time with everyone on the team, collaborative environment, there's always help if you need it. Furthermore, if you're interested in pursuing a project that may fall outside your specific job description, its highly likely that you'll be able to take a crack at it.
Cons
Sometimes tasks are not spelled out clearly for interns, so there's some guess work involved when you can't get in touch with the project lead quickly. The negative of having a small team is that if you don't like some of your coworkers, you will have to deal with them a lot. This wasn't a problem for me, but other coworkers of mine had some issues. Since the company is an NGO, the pace of projects can be very slow as there isn't the funding or manpower to expedite, so if you like working on fast-paced tasks with quick turn over times this isn't the place for you