Pros
Generally your peers will be well educated and the work schedule is extremely flexible. If you are a SME and looking for a company to stick with comfortably until retirement then MITRE would be a good fit. Older employees have ample opportunity to either carve out a niche or build their own work programs with a variety of different sponsors. Their education reimbursement programs are good and until recently the retirement program was top notch. Workers are fairly secure in their jobs, and turnover remains in the single digits.
Cons
The company has an abysmal track record keeping its best and brightest unless those individuals are happy in their project space, leading to 30-50% year-to-year turnover in fields considered up-and-coming in the market. The company claims it would like to move away from its average age of 50+, but in the same sentence says it is not willing to pay industry average in that experience range. If you are not exactly aware of how the salary increases are structured you can easily end up receiving below inflation raises regardless of the level of work produced, and it will never be corrected unless you leave the company. If you have the misfortune of ending up in an inexperienced department, it can hurt your ability to land relevant work and get promoted. This in effect creates pockets of pronounced backstabbing and favoritism that fall completely in opposition to what the company stands for. The lack of 360 reviews means many of these problems will never see the light of day. As many others have said, a good number of managers are placed there with only technical experience under their belt and have no idea how to actually manage a group of peers. Instead they tend to divert back to primarily project work, do the bare minimum in work shaping, development, and assessment meetings and hope that flies.