Pros
This is a tech startup company so you can learn much more than if you were in a large corporation. You will wear many hats and can cross over swim lanes. It's encouraged, which is the opposite of many companies. You are told to address the issues you think need to be addressed and awarded for your initiative. Having an entrepreneurial mindset is an asset. People are very smart, work hard, and are sincerely nice. Being earnest and nerdy is part of the company ethos. The company is socially and environmentally conscious. The office is nice. Some might even call it trendy. It's within walking distance of two train stops and is easy to get to. The work is dynamic so you will go through many projects, exercise your technical capabilities, and be constantly in learning mode. The leadership team is approachable and hands-on. Don't be surprised if you're working on a project with the CTO or CEO. The company is committed to the people who work there. Many people have been with the company since its inception, and not all are in the leadership team.
Cons
The company is small so you won't have some of the amenities of a large company (e.g., workout room, cafeteria, etc.) but you are in a trendy part of Chicago (Lincoln Park, Buck Town) so cool things are within walking distance. The priorities change quickly so you have to be in tune with the leadership team and be prepared to pivot quickly. If you are expecting the structure and organization of a mature company, you will be disappointed. This is a tech-heavy company that values engineering acumen and effectiveness. You have to be on top of your engineering game.