Vantaggi
Their salary rates tend to be pretty competitive with the market. They have a strong emphasis on project management (as opposed to letting the creative team run the show) - so you may have better odds of keeping the project on track for whatever deliverables you have. However...
Svantaggi
..Management has unrealistic expecations of resourcing. (ie: only 1 UX guy, let's give him 5 deliverables next week! We have to, that's what we promised!) This could be said about many agencies, but it gets old fast. Also, management owns the company. They decide how they like things done, it's their money, it's their friends in upper management. This can be really toxic because any complaints you have on upper management will mean on the next round of layoffs you're "it"... very clique-ish in this way. I hear it's improved in the last year since the former creative directors have left, but be aware.