Pros
I worked for ManTech 15+ years. During that time, I was on 5 different contracts and once had a lag between contracts for about 4 months. They always helped me find another position within the company. Pay was average. Coworkers were mixed bag - from great to not very great. I'd work for them again. Working on site for customer was different than working at a ManTech building. I really enjoyed working at the ManTech buildings. Very casual and positive environment.
Cons
twice during my 15 years there I was put on contracts where the job I was given had very little work to do. ManTech didn't seem to care because the customer was fine with it and they were getting paid for me sitting in the chair. I was so bored I was going bonkers. I like to be busy and learning so this was a con for me. I also thought it was a waste of federal tax dollars (contract with federal govt).