Pros
Founding technical leadership is awesome. Most Fastly folks — especially outside of Sales/Client Services — are friendly down-to-earth people. Flexibility (typical of SF/Silicon Valley tech culture) No “bro culture.”
Cons
If you are looking for a cool startup to join, look elsewhere because Fastly is not it anymore. In particular, there is nothing cool about the Sales/Client Services org. Salary: Most likely the equity offered will be insignificant. Also, your bonuses and accelerators can be screwed with at any time. If you want to work here, make sure you negotiate a base salary commensurate with your market value. Don't rely on anything else. Bias: The small size of the company facilitates development of more personal relationships (as opposed to strictly professional relationships). This increases likelihood of bias in evaluation of reports of discrimination/wrongdoing when the accused is a part of the immediate circle of the person evaluating the report. There are definitely certain people who are a part of privileged circles at Fastly and can get away with unlawful behavior, at least the first time. Culture: Typical western liberal culture. (This is not exactly a con, but it's not ideal.) Fastly does not have the cultural diversity of a global tech company.