Pros
Can't Find any, except if you are on some kind of time based visa in the US - like a student OPT or H1B with limited number of unemployment days and you desperately need a job, then maybe you can give it a thought. If you have an active offer from them, just accept it to save your visa status. Work for a 3-5 months and you will understand, what I am trying to say here !
Cons
Since it is a small firm in the US, with no physical office locations, except some shared office spaces in some locations, you actually never get to meet the people you are working with, even once. Fun fact - in the tenure that I worked with them, I never actually got to see the faces of the people I worked with. There were some annual summer picnics arranged and people showed up , but they were from other teams. If you are coming from a good corporate culture, with standard ethics, you will miss that greatly here. Forget Ethics, they don't even know how to handle standard HR processes. I don't even want to start about the work culture, it is a process where they over commit and under deliver to their clients and believe me their clients are not happy with them and its the associate or junior level employees who are suffering. Since clients are not happy with the overall work, their whole attitude towards the team changes !