Pluspunten
Work life balance is good. When I was there, there was not that much pressure to deliver, but this can also be a con because your skills and career development will flatline.
Minpunten
Promotions are largely dependent on tenure and playing politics and not so much on your skills and impact. Because of this, the incentives are not there for people to work hard. There are many many people who are merely coasting and contributing the absolute minimum to their project; essentially only speaking up in meetings when they are addressed and doing the minimal work necessary to get by. For anyone somewhat ambitious in their career, this atmosphere is stifling and extremely painful. Even though I did not have much work week-to-week, I was very burned out when I left as I had lost all interest for my work. Although there are smart people at MITRE, on average, the intelligence and drive of the average employees is nowhere close to those in Big Tech. This may be a good place if you have a family and/or close to retiring but I would not recommend it for someone starting off in their career, unless they have no other options.