Pros
Great company to intern for. Interns have the same expectations and responsibilities as full-time engineers. Practices are geared toward quality documentation and code reviews. Cofounders are actually engineers, so they're not just setting the vision and then disappearing. Team is very friendly. Small team means you will learn about the whole product and see both engineering and business perspectives.
Cons
High expectations, high stress: I burnt out badly, and showed all the classic signs, but my boss was not willing to work with me on that. He just said, this company has very high expectations for pace of work compared to other tech companies. Team wants to move fast, but the product is already on the market and there's not much on the to-do list. This meant I worked really hard to build projects that didn't really improve the product. At times, I was managing two projects at the same time with the expectation that my individual contributions would remain high. I told my boss I wasn't ready for that and was only offered the advice to do my best. Small team means there won't always be someone who knows how to do X. For "more senior" devs (over one year of total experience, still a junior at most companies), you're mostly expected to figure out everything on your own. Asking for help was explicitly encouraged but senior engineers definitely seemed annoyed when I asked for help on more challenging or ambiguous problems.