Pros
People here are super intelligent and friendly, and they respect your professional skills. I never got a No of any favor asking, and I learned so much from them. The teams have a great process and keep iterating on it. As a designer, I care a lot about ownership. One of MongoDB's values is "own what you do" which can be strongly felt. Collaboration and teamwork are my favorite part. Not only within your team but a lot of opportunities with people outside your regular teams - lots of activities like an internal hackathon, game week, lunch & learn, social time, and group learning opportunities. It's growing globally and it's a brand you can talk about with pride.
Cons
Since the company grows so fast, every team will spend significant time on interviews and onboarding new members. Finding the right people is not easy. Also, the title and compensation system might not work as mature as FANNG (or MATE?). If you work on some complex product lines or projects, you might experience some politics (which is not bad if you are good at it).