Pros
You get to be surrounded by people who want to work hard and get things done. As a developer, I got a wide range of experience in product management, frontend, backend, devops, and testing. I love learning so this was a good place for me as there were so many different opportunities to gain knowledge. I never got bored from being on the same problem for too long. Management was understanding and would allow me to work on problems I was more interested in.
Cons
If you're not self motivated this company isn't for you. As with most startups you really need to provide value as money is more scarce than large corporations. If a contract is completed or lost then job opportunities potentially are lost as well but if you work hard there is always a place for you.