Pluspunten
There is a big push to do important work at MITRE. Constant badgering about "what is MITRE work", versus SETA work. There is pressure to provide "impact" for the sponsor, rather than just run job hours. It is not enough to have a project to work on, you must be providing serious sponsor impact. The retirement program is good and the vacation is good.
Minpunten
The combination of not-for-profit, minimal growth, and very low turnover limit career growth opportunities. I would stay away if young. MITRE provides senior technical advice to the government, and age and experience provide confidence to the clients. Perfect for those at the end of their career who have already been senior managers and don't want the pressure any longer. However, even in those cases, you must have some serious techical ability or specialty.