Pros
I worked at Synack for a little over a year. Most people are nice and operate with a constant background of intensity, pressure, and anxiety. This might very well be the norm in the security industry. It's a fun and constantly evolving challenge for those who really like it. There are catered lunches everyday but this seems to be less a perk and more an expectation in startups nowadays. There is decent secular growth in the security sector and the co-founders seem like they might know what they are doing sometimes.
Cons
The executive team ranges from generally up-beat, mediocre leaders to downright toxic. There are happy hours on Thursday's but the teams are generally new due to higher than average turnover for a company its size. There is no cohesion between different teams. There is a lot of miscommunication and lack of prioritizing what's important. A good chunk of employees are young and fairly inexperienced in the space. The company has a "learn-as-you-go" attitude but this approach is a failure on leadership's part especially because it's now well into series B. So don't expect on-boarding because it will be disorganized at best. There are members of the exec team that have a toxic leadership style that rule by intimidation, act in a disorganized and impulsive behavior, and seem to thrive on public disparagement, which ultimately tears down team morale. There is no strong path for long-term professional development and little in the way for the company taking serious investment in you unless you are in R&D. There is almost a de facto burn and churn mentality. This is not a sustainable business model and neither is outsourcing most of the security work to researchers in foreign countries like India and reselling it for a lot more to domestic clients. Overall, the teams feel disjointed and the culture, although mostly friendly people, feels hollow.