Pros
It looks good on your resume, because somehow word hasn't gotten out yet that this is the worst disaster in the industry.
Cons
The ONLY criteria for your job performance is how much attention you've gotten for the agency. Seriously. It states this point-blank in the self-review form: "How did you make us famous?" Things that are NOT valued include: doing good work, delivering what the client needs, being collaborative, fostering creative talent, or being a good teammate. Every project is utter chaos. There's no process, because the people who run Mullen think process is somehow antithetical to good creative. When a piece of potentially interesting work comes around, everyone swarms it. This competition doesn't result in better work, it results in people being awful to each other. There's no opportunity for advancement, and no prescribed path to raises or promotions. Upper management barely makes an effort to hide the fact that they are intentionally, proactively postponing and canceling reviews. When you win awards for the agency--even though they explicitly value only this--don't expect any thanks, and certainly there won't be any raise, promotion or bonus (even though most offer letters mention frequent spot bonuses--these have never occurred to my knowledge). Mullen has the deepest, most ingrained sense of entitlement I've ever seen, and the upper management sees praise, awards and accolades as its due. When you do good work and win awards, they're merely satisfied with themselves that they're getting what they've deserved all along. It never occurs to them that some people actually made these things. They only notice you when you fail to hand their awards up the ladder to them.