Vantaggi
The work at MITRE is fairly unique. You get to work on government problems that you don't often have access to at any other company, including typical government contactors. Most of the middle management (Division and Department Managers) are genuinely good bosses.
Svantaggi
Since ~2021, the upper management (CEO and SVPs) keep making small incremental changes that are bad for employees. Quiet layoffs, reduction in benefits, reduction in vacation time, ham-fisted attempts to force people back into the office. Through all these changes, the attitude from above hasn't been transparent, apologetic, or even solidarity. It tends more toward "quit your whining". Additionally, MITRE's previous focus of "working in the public interest" seem to be fading, much like Google's "don't be evil" mantra slipped away. Corporate moves seem to be emulating commercial companies rather than MITRE's history of non-profit, public-interest, above all else. One example: raises for levels Principal and above are now tied to corporate goals that are hard to affect for anyone below a VP level.