Pros
I was an employee of Mandiant prior to the acquisition by FireEye. I don't have many good things to say about FireEye so I won't attempt to.
Cons
Once acquired the FireEye staff and management team didn't listen to or take any advice of the experienced Mandiant folks. Once the layoffs happened nobody from Mendicant was given any thought to the hundreds of technical positions that were posted only showing us the door. While the severance was generous their lies about being reimbursed were totally uncalled for. All I can say is keep your resume up to date, your contacts in order and DO NOT take these jokers at their word. Dave Dewalt talks a good talk but you can see his lies in their stock performance. Look at the unbelievable climb after the acquisition only to drop well below after a few weeks. While the pay was good, you never know when the layoffs could begin. Everything looked great up to the last week.