Pros
-very interesting technical problems -individual contributors overall are really great to work with. generally good people who are also smart, motivated, and hardworking. -lots of ownership over your work. in true startup fashion, if you think something should happen (technical, company, or otherwise), you have more power here than at bigger companies to enact change -direct access to upper management and the founders is easy. I know of several instances where feedback I or someone else has given has been heard and acted on.
Cons
-as the company grows, communication has suffered. leadership has recognized this problem and has taken visible steps to address it, but still a ways to go -there is far more intense scrutiny on IC work by higher level leadership than I've seen at other companies. I attribute this to the company being relatively small with only one product to focus on. -I know of instances where I or others did not feel comfortable giving feedback to leadership -lots of churn and stress to try to hit short term goals at the expense of having an extended vision (and therefore time) to hit long term goals