Pros
Fastly is one of the smaller companies I've worked for, but at the same time one that acknowledges it has a big role to play and works hard to live up to it. Fastly runs a significant amount of internet traffic every day, and because of that it's a great place to do hardcore engineering, and come up with innovative ways to speed up and protect the delivery of internet content. Other companies where you can do similar things are likely to be significantly bigger, and have more barriers to making big contributions as an individual. What I have liked in Fastly is the responsibility each of the employees takes for the success of the company and its customers. I've worked here for close to a year, and still haven't seen much of a "pass the buck mentality": when someone raises a problem, colleagues will take ownership to either fix it, or find someone responsible to fix it. Especially during time critical issues, the entire company comes together and makes sure the right things happen. Making sure customers are taken care of is something everyone sees as their responsibility. In addition, the employees and leadership are genuinely nice people who treat each other well. While I don't see money being spent on unnecessary, frivolous benefits, Fastly spends a lot of time thinking about its culture and figuring out nice, unexpected ways of reinforcing it.
Cons
The company is at a specific phase in its growth where process is at the top of mind, and is being carefully considered and implemented, which is a stage that may not be ideal for everyone. However, I feel all of this is happening with a great degree of maturity that is setting the company up for long term success.