Pros
Lots of freedom to work on projects that you find interesting. TONS of support from coworkers and supervisors for new staff. I felt really welcome when I started. Flexible hours, and work from home options are a plus. In general, people really care about the work that they're doing and want to make a positive difference in the world.
Cons
The work can be fairly isolating. While each team is collaborative, very little teamwork occurs in-person. Instead, everyone spends tons of time sending emails and talking to each other over the phone. It can be draining to sit in front of a computer and not meaningfully interact with another person face-to-face for days at a time. Additionally, while the company is making real progress with issues of diversity and inclusion, it still has a ways to go with fully integrating a comprehensive understanding of social justice in the workplace culture. That said, I don't know of any other company in this sector that's clearly handling these issues better, so this is not much of a con. Maybe with that context, this is a pro, since Mathematica appears to be ahead of many other orgs even though it's not enough.