Recently out of stealth mode, exciting opportunities and prospects
Pros
Company is a well-managed startup where the excitement isn't dampened by the enormous stresses of shipping the first product (it's already out the door and in use by customers) or making payroll (the company is well funded and has paying customers). Benefits are good for a small company and presumably will get better as the headcount increases so that they become eligible for higher-tier plans. Management encourages personal responsibility with respect to vacation policy, managing workload, and taking on challenges -- good for people who can self-manage and have the follow-through to see their vision through to completion. Company prospects are quite exceptional -- there is enormously high demand for the product, which seems to be defining a new product genre and (currently) has no public, credible competition.
Cons
The hierarchy is relatively flat and people who require a significant amount of management hand-holding or technical support to be productive may find themselves lost. The company's internal security is necessarily commensurate with its product, and people inside the company do not have the wide-open access/visibility to all the source code, documents, etc. that people might expect from a startup. People who want to work-from-home a lot will probably be disappointed, as the company is moving quickly enough that being physically present in the office daily is necessary to be productive. (Physical presence is necessary in part because of the limited access/visibility -- work requires a bit more coordination across these boundaries, and that work is done largely in person, which may be a turnoff to people who don't like to communicate verbally with coworkers.)