Pros
SpaceX has a great mission and Elon and Gwynne really care about the employees and making the company has fantastic elements. The mission to Mars is amazing and it's breathtaking to be on the front lines of transformation technologies like reusable rockets and BFR. Management mostly cares about work life balance although its working 60 hours or so is still the norm.
Cons
The purity of "meritocracy and mission" pretty much stops at Elon and Gwynne. Right below them is a litany of , directors, managers, and leads, that constantly are in political battles. Coming from big aerospace this is normal, but SpaceX is supposed to not be big aerospace, so the trend into middle management kingdoms is disappointing. As an engineer actual advice from my manager was spend more time on weekly update emails and confluence pages because they need it advertise work to other engineering leads and managers. As an engineer it seems as though if you're not promoting yourself or very actively networking within the company you'll be passed by on projects and promotions. Again this is normal of bigger engineering companies but SpaceX constantly advertises itself externally and internally as a "meritocracy" that focuses on results. To illustrate this SpaceX now has 3 to 4 layers of management between Gwynne and the individual engineer. If you need to collaborate from someone in avionics or in the internal ERP team without the buyoff of 2 leads, 2 managers, and maybe a director, good luck. Another way to put this is, if you need to get one day of technical work done expect at least half a day of meetings minimum to "align and set expectations" At this point if you're looking to succeed in the engineering industry more based on your ability to change reality and less based on your ability to sell people on the "great work you did", I would suggest applying to real startups like Relativity Aerospace or RocketLab, where the team is small enough that you don't have to spend 5 hours a day going to meeting and another 2 hours making internal billboards telling people how cool your work is. SpaceX unfortunately is becoming very much like the larger companies it itself is upending. Not necessarily a bad thing but adjust your expectations before taking a role here.