Pros
You will most likely get a security clearance which is valuable. The work you do is usually really interesting and impactful. Great experience to use in your career trajectory. I think the benefits were on par with what everyone else offers. They do offer more than most companies for education.
Cons
Let's see here... unless it has changed if you start as an Admin, you're stuck. Even if you get a higher degree they discourage allowing you to switch to the research track. They will treat you like a peon. It can be incredibly cliquey and catty. They love to hold on to incompetence and allow that same incompetence to remove anyone who points it out. There's a lot I could say, but I do not have time to write a novel about the poor management of a once great company. Take a job and find out for yourself. Hey, maybe they changed and it is great again, who knows. Prove me wrong.