Pros
A very fast growing start up. They got recognized at various global events. Very different idea on which they are built. On technology, various technologies to work on. Very smart, intelligent and energetic people to work with. Since they are in early phase, you get to see things closely. Adventures and thrilling experience almost every day. ;-) It is a good place for freshers to learn at the start of your career.
Cons
Well, everything in this world has a cost attached to it. Here, they don't care about you. All they care about is the company. You might be useful today and not tomorrow. You are good God today, a switch of events and you're out of the picture. The top order decides almost everything and leaves so little for the rest of us. There are many things to work on, various type of technologies, different type of strategies, but if they don't feel you are 'worthy-enough' or someone else is 'better', you won't have it, even if you were the one who introduced that. They need you today, you will be loaded with the responsibility of entire project, tomorrow they found someone better, you won't even know when things got changed under your nose. When it comes to working, you will be told to work as Google-Facebook-employee... consider yourself no less than Elon Musk. When it comes to package, your previous package decides current one. They might fire you and ask you to pack your things in two days. But if you are leaving, you might have to struggle for your last working day. Been there! If you believe in 'that's how the world/startup works' even if it happens to you, go ahead. Advice to new recruit - Make sure you have all things clear BEFORE joining, things like package, shares, perks etc. Don't go into things like 'we will give you this after XYZ months', 'it's a probation period' etc. If they are not sure about you now, chances are they are taking you in till they find a better match. P.S.- I am assuming that you are ok with ~70 hours a week, 6 days working culture.