Pros
Working with great people. The projects are from all different industries, great variety. Working with the cutting edge of machine learning technology. Lots of opportunities for learning, for leadership, and for excellence. Work-life balance is good for a startup, people aren't expected to work themselves to death. Compensation is good, it's a well-funded startup and people are paid a good salary and and not just promises of future greatness. The vision is, nevertheless, very ambitious.
Cons
It's a startup - things move very fast, you'll be expected to jump right in. Expect to wear many hats - which I am mentioning here as both a good thing or a bad thing, depending on what the hats are and what your career goals are. Scope of software is rapidly expanding, and clients often want things now now now.