Pros
Job stability if you exclude the fact that many employees, due to the lack of management support, need to look for projects by themselves, often resulting in using personal/vacation time, frustration and work of random projects.
Cons
Anyone looking for professional development and growth should avoid this company in a wide circle. The working culture is very much the opposite of what is being advertised. In a nutshell, lack of opportunities to work on challenging projects and develop technical/leadership skills and lack of cooperation among peers and different groups lead to professional stagnation and unsatisfaction among employees. Since many people at MITRE have never worked at any other company, it is relatively easy to sell them a story about how great MITRE is. This virtually unknown company even gives itself a right to compare itself with big tech giants such as Google or Microsoft, but 99% of people there would not survive on the competitive job market. People's skills get quickly obsolete due to the lack of proper training, project opportunities, and desire to stay current. In many cases, managers are young inexperienced people who didn't have time to develop the necessary skills to lead a group of scientists/engineers but are selected based on their cultural fit. This is only possible in a place where ownership and accountability are low, and there are no consequences for the job not done. If you are a mid-career professional and have an advanced degree (MSc, PhD), and still want to join this place — make sure you understand the level at which you are hired. You will most likely end up at the same level as kiddos with 2-4 years of experience after college. As you will be considered too old, you will be overlooked for job promotions, and needless to say, your salary will not even catch with the inflation.