Pros
Everyone is excited to be here and wants to contribute, help, and learn new things. The flexibility is great and you are treated as a talented employee without need for micromanagement - there is a lot of autonomy in your work while also having great co-workers that make asking questions easy! There is also a ton of opportunity to get involved in new projects that expand your knowledge and experience base - the work is different every day which makes time pass very quickly and you learn a lot!
Cons
Quick turnarounds are needed on tasks and things can change often, sometimes requiring a pivot on your part from what you may have been working on or already completed. All things to be expected in a start-up but it may be hard for some. It is not a job where you can expect the same day in and day out if that comfort is preferred.