Pros
You will learn a lot about immigration law, business immigration law that is, at Fragomen because you will be forced to. Maybe you will be lucky to get a good manager who will teach you something and not leave you to sink or swim on your own.
Cons
Fragomen works hard at hiring young people from top-tier schools and almost always has openings. You're interview and first week will be a honey-moon (the HR department courts all its new APs) but then will have to hit the ground running. Welcome to corporate slavery. Fragomen has a high employee turn over rate an less than 50% of Assistant Paralegals make it through 2 years. You will have to do a lawyers job at Fragomen whether your a paralegal, legal assistant, or simple team manager (people who are meant to manage mail correspondence). You will get no useful training whatsoever to complete your tasks and manage the responsibilities you have for your caseload. Caseloads are inconsistent, rushed, and rarely manageable. There are few Fragomen paralegals who go home on time and its more rare to go home completing all of one's work. Team leaders frequently put client opinions and wishes (possible or not) before their employees well-being and rarely take into consideration what is reasonably doable in a day's time. All "lower" employees (non-lawyers and non-CSMs) do repetitive work literally filing out paper work all day in front of a computer screen. You will not be taught more than the bare minimum and will rarely interact with your clients (lawyers and CSMs take credit for all of their team's work on the client side). Talking with fellow employees is highly discouraged by team leaders who would chain you to your desk if they could. It is not uncommon for people to work through their lunch (which is time you are unpaid and clocked out) because they are afraid of losing their jobs. The expectations of partners and associates are unattainable. You're expected to know everything the moment you step in, even if you have no background in law, no JD, and no experience with immigration. You are given full responsibility for your cases (lawyers do little or no work besides signing papers and billing clients) which is a very scary thing when you are dealing with people's legal status in the U.S. This is a burn-out job. You'll work long hours for leaders who severely underrate and under-appreciate your work. I have also heard Fragomen paralegaling called the "black hole" because many people are so miserable but have become so pigeon-holed in their positions that they cannot escape.