Pros
The pay was very good in the past, especially because NATO contractors outside the USA can avoid most income taxes. However, the pay has come down in recent years. If you want to live overseas, this can be a great way to do that.
Cons
GDIT's business is to win US government contracts and staff them. Employees are assets which are used to staff the contracts. The company doesn't care about its people, but that isn't unusual. If you accept a job overseas, the company will pay your moving expenses. If you quit the job before the contract ends (typically 3 years), you may need to pay to move your things back to the USA. That could cost a lot. Working with the US government and military is very bureaucratic, very political, and very chaotic. This is almost entirely the fault of the US government and military. What might take a small company 6 months to do will take a contractor like GDIT 2 or 3 years with many project changes and even cancellations and restarts. It's a frustrating environment for someone who wants to accomplish something.