Pros
Working at MongoDB means working with the smartest and most talented people in the industry. Which led to the huge growth of MongoDB. I enjoy being part of this success story, not only because I believe in the technology and our products, but also because of the people and our company culture. In my role, I get to make our customers successful in using MongoDB by helping them with all their technical challenges and also by educating them. This can sometimes be really rewarding, to be able to solve something that had been a big issue for a customer or to see how somebody turns from being a MongoDB noob to an expert.
Cons
The downside of working in a fast growing company is that everything is always changing very quickly. Which sometimes can lead to problems, but often it is also an opportunity to improve things.