Pros
Free catered lunches! That was pretty cool. You also get free food around the office (so breakfast) and dinner if you stay past a certain time (so always). And HR hosts a lot of events with snacks and drinks.
Cons
The people at Flatiron are undoubtedly very smart, but they are extremely pretentious about their educational and work backgrounds. Many people are coming directly from PhD programs, bringing that culture over and lacking an understanding for what it means to be in the private sector: how to work with other employees, and how to grow talent. Work culture is terrible -- 12-14hr days are normal, and if you're working less than that, then you are clearly slacking off. Managers are cliquey and inexperienced. The company has grown very fast and they are having issues scaling. New people join every couple of weeks and very little is done to get them on-boarded. There is little training on the subject-matter and poor mentorship and leadership. Flatiron has a great mission, and their employees are passionate about that mission. But because of this, politics and internal investment are often overlooked.