Pros
This is not a place where you coast; it's a place where you build. If you want to solve hard problems and see your work shape the future of a product and an industry, this is the place for you. We are building something great here and not just on the product side, I mean on the marketing / communications team. We encourage everyone on the team to jump in, help out, and debate to get to the best possible solution. Because of this there is room to grow / build out capabilities across other disciplines. I'm amazed at what we can accomplish in 2 days that would otherwise take weeks at previous companies.
Cons
Primary "con" if it is one, is the inverse of the "pro" of building something. We move fast, which means you have to be comfortable with a degree of ambiguity and be highly adaptable. We are getting to a much more organized place compared to when I started, but there is still a lot room to grow.