Pros
If you land with a good team and good customers you will enjoy your work. There is also a lot of opportunity to move from contract to contract or change customers. Also a lot of corporate engagement and training if you seek it out. Senior management also is extremely accessible and makes an effort to engage unlike a lot of other companies.
Cons
Program managers of large contracts often have no idea what their folks on the ground are doing, which can be good to not be micromanaged, but also they are then not aware of how embedded and valuable you are to client. So, when it comes time for review or any bonuses, their lack of awareness results in minimal raises or additional compensation. They also need to know that "one size" doesnt fit all, because so many of the Serco workforce are second or third career professionals (retired military, govt, etc.) so asking "where do you see yourself in five years" kind of is a moot point and lacks managerial awareness for someone with 30 plus years in the workforce.