Learn a lot, Tons of Responsibility, Smart People
Pros
Most projects at Acumen are really very interesting and have an impact on public policy. You work directly with people who are deciding policy and regulating healthcare in the United States, and more often than not, your data analysis and suggestions to clients are received well and are highly valued. As a whole, the people who work here are really very smart. Bunch of Stanford/Cal/UCLA/Ivy League grads who care about the job and would rather work on fascinating projects instead of writing code for a startup trying to sell more ads online. The workforce is very young (lot of people out of undergrad/masters programs) and it's very common for coworkers to hang out with each other outside of work. If you are someone who is quantitatively capable, a solid communicator, and are good at creative problem-solving in a team environment, then you should expect to be given a good deal of responsibility fairly quickly. These employees advance quickly in terms of position/salary, and it is possible to be managing projects after a year or two of working at the company.
Cons
There are still some areas of the firm where the culture is such that it encourages long hours, but this has markedly improved over the last several years and continues to get better. If you happen to be on a project run by the CEO, it can be grueling and not have much direction or shifting goals. The projects are usually very interesting, but they often run right up against deadlines and are not very effectively managed. You are not going to get the traditional Silicon Valley perks of free organic lunch and dinner and free dry-cleaning etc. that has become pervasive in the area. However, that is more a comment on the spoiled nature of the tech scene and less a con about Acumen. Nevertheless, that is the competition.