Vantaggi
The coworkers are really committed, and there is a strong desire to build a great product. The technical areas have the most talented people I've seen, and they've built a something really good. The problems tackled every day are as complex as they get, and the solutions are impressive. As a product, it's innovative in an industry where most big players aren't.
Svantaggi
Leadership is a big hit-or-miss. You either get a great leader that helps you grow, motivates you and helps you get better and do great things, or you don't. If you don't, be prepared to be ignored, micromanaged and simply dismissed as another grunt. The company is growing, but it has no control and no structure. You can make things happen, but usually it is through very hard, unrewarding work. There are no schedules, you can arrive and leave at any time, but most of the time, you will have more things to do than hours are in the day, and the deadlines, code merges, meetings, won't be moved.