Pros
Excellent place to work if you are ambitious and want to grow your career. Best part of the company is that they promote based on merit and ability instead of time spent in a role, meaning that if you prove yourself early and often, you can expect advancement quickly. Furthermore, they are quick to create roles that currently don't exist if you can prove that there is a need for that role, so you aren't tied to some archaic org chart with delineated paths of advancement; you can be a 'pioneer' and start your own path. Finally, despite the accelerated growth within the organization, they still maintain the mentality of the start-up I joined years ago. Not bureaucratic, welcoming of all ideas, and things move incredibly quickly.
Cons
Not necessarily a con, but since we maintain the start-up mentality, things can change rather quickly. You can be working on a project one day for an initiative, then have the entire initiative scratched the next and be moved to something else. If you are the type that likes a clearly defined path forward that is nice and neat and moves at a consistent pace, probably not the best place for you to work.