Pros
Because they're so big, they have the capability to pay higher than most credit unions. Usually, though, they start you at the bottom of the pay scale.
Cons
PenFed is not a great place to work. Employees do not communicate with each other, or with the business unit. They want to push projects out quickly, but all the red tape means things happen VERY slowly, even maintenance. They want to grow for the sake of growth, but that growth comes at the cost of the employees. When they acquire another credit union, they're mission is just to absorb the assets and membership count. They have no interest in the employees, or for that matter, don't care what happens to them. PenFed has shady business practices. It is a VERY high stress environment to work in.