Pros
Tons of opportunity for growth - it's a startup that rewards problem solving, collaboration, and delivery/execution. There will be ambiguity but that's what you sign up for when you join a startup. The org is flat and great ideas come from all levels/teams. Mission-driven which is really important to everyone and I feel I'm surrounded by really smart people.
Cons
Classic startup struggles - tons of great ideas but we need to focus on prioritizing, rather than letting it distract. Communication across teams can be improved but I'd say every company struggles with that as it grows. It's something leadership is aware of and is working on. Benefits are good not great. I don't see these as a 'cons', more startup things to be aware of. You don't join a startup for benefits, you join for the growth opportunity.