Pros
Great work life balance. Low to no responsibilities or tons of responsibility based on what you're comfortable with. Noteworthy employees are self motivated and great to work with. Introduction to some data science tools and techniques. Tons of freedom to innovate and create, but little to no direction. Tons of job security, and a stress free environment. This has led to some funny stories of major mistakes and no one gets in trouble. CEO is very candid and personal with employees. Everyone knows everyone and they all get along. Office rumors and gossip are very innocent and not malicious.
Cons
There is little to no training for new employees, and you need to be self sufficient to be successful. Everyone knows about this, so you can accomplish nothing for an extended period and still be considered "successful" in the company. For a very small company there is little visibility. You'll have to struggle to work through the ranks, but a long time employees working in Excel will be commended when they find out conditional formatting can automate their job. The tool set was cutting edge when created, but due to years of slow updates, everything looks and feels old. It's like a Back to the Future concept of cutting edge (cars can fly, but they still use leaded gas). It's an open office, but half of the employees have offices. Open offices are meant to make a collaborative work space, but this alternative makes an uncomfortable and obvious divide between employees and "managers". Looks like a call center or factory that recently unionized and not a collaborative anything. If you are in trouble, you won't be told directly. You'll be called to an impromptu meeting with whoever is in the area when the meeting is planned. Then everyone will be congratulated on their work but you or something similar. Very passive aggressive, but also pretty funny.