Pros
Great learning and training opportunities for those who are capable of managing their own careers. With enough initiative, there are plenty of options to move between different roles or work within different client groups if one wishes to widen their experiences - however one must be proactive to take advantage of this. The people make it - many senior managers who are genuine, friendly and willing to support younger consultants, although changing a little as more of the 'old-guard' are moving on as the company expands.
Cons
Despite operationally being a little removed from the parent company, one must be comfortable being on the payroll of an arms manufacturer. Some junior consultants who are yet to work out their career path have difficulty finding their place in the workforce without suitable mentors to guide them, although I hear that the new graduate schemes are doing more to improve that.