Pros
There's a natural push to hire and promote from within. SpaceX does not limit anyone's career - it's actually 100% in your hands. If you want to be challenged and constantly work on new projects, come work for SpaceX. Compensation (salary + equity) are highly attractive. Excellent benefits. Last, clear and direct communication with upper management. If you're an Engineer I and you have a solution to help the company, you can go directly to Directors and VPs, even Elon! Zero red tape and no bureaucratic BS. Let's build some rockets - to Mars!
Cons
Awareness not con: SpaceX is a flat organization, meaning, managers and directors work as individual contributors and drive production. Be prepared to own your work as if Elon has to personally sign off on everything. There's no cutting corners. Anything short of perfection, will lead to disasters and/or failures.