Pros
MixRank is fully remote, with people from various corners of the world. The team is composed of a small number of skilled people. There are no jerks and everyone is pleasant to deal with, including the CEO. There is a good amount of autonomy and trust in the work and async communication is used well. You'll have the chance to contribute to all parts of the stack. The CEO is also a DBMS whiz with solid knowledge of Postgres internals, which is the primary driver here. So there's a good chance to up-skill on that front while you understand the ways in which it's been used. The data managed by the company is also very large, so there are interesting challenges and solutions there as well. There's also a ton of enhancements planned on the product side, so the future is pretty bright.
Cons
Perhaps nitpicking, but like with any other long-lived company, some legacy code issues. But since the CEO is also a programmer, this is not ignored and there are plans in the roadmap to address it.