Pros
Fantastic staff, really care about professional development for interns (so much so that they call them "Program Associates"), many opportunities for growth inside the organization. Very flexible; young and fun staff. Small organization so you get a lot more responsibilities and opportunities to step up; also many opportunities to meet/network with institutional member bigwigs.
Cons
Pay is low for interns (stipend instead of hourly, and prorated based on how long you'll be there). BUT opportunity for bonuses and lots of fun benefits like work happy hours/meals. Also nice to be paid in the first place, so not a big con. It's a small organization so they're doing what they can.