Pros
EB's affiliation with Edelman, which is well-respected and has a great client roster. However, the culture within Edelman Berland is so toxic that it outweighs these benefits. If you're serious about a career in market research, working for EB would actually hurt your future career prospects. If you know you want to work in public relations, pursue work with Edelman directly.
Cons
This used to be a great company, but two CEO changes, first in 2011, then again in 2012, completely overhauled the company's philosophy, business model, operations, clientele, and culture. Change in inevitable with any leadership turnover, but nearly every change implemented in the last 3 years has been to the organization's detriment. Company leaders encourage pettiness, gossip, and passive-aggressive behaviors. The culture is absolutely toxic. Most of the talented employees were either pushed out, or treated so terribly they left on their own within 2 years. The CEO is not a leader, he's a dictator and a jerk.