Vantaggi
They get a lot of contract work and they partner with their parent company, Accenture/Accenture Federal Services, which ensures a deeper pool of opportunities when contracts end. Nothing is guaranteed, but they do make effort on your behalf and intend to help people get subsequent roles when previous contracts end. I've spent about a quarter of my career supporting contracts they own and they are consistent about holding on to good assets, and generally do their best to keep folks for as long as possible.
Svantaggi
Part of how they get so many great contracts is quality of service combined with competitive pricing. Competitive pricing means lower average pay on the scale for a given area, while demanding a lot of experience to comply with contract requirements. So on the one hand it is not the maximum pay available in the area for the same work, but the trade off is a little more job security than with other organizations who will pay you more and then immediately lay you off if they lose the contract you're on.