Pros
Mercer is a top human resources consulting firm and it's all because of the people on the ground (sales, producers, consultants, analysts, admins). You will be challenged to think strategically, and you can expect to learn a lot about how to deal with demanding clients and internal stakeholders, all of whom compete for your time.
Kontras
The approach to training new hires: throw them in the fire pit and see if they can climb out alive. Teams are also kept very lean. It seems there are a lot of consultants to give free work or heavily discount work to clients, and that leads to unprofitability, which in turn compels leadership to further cut down on headcount. Then, those who are left behind are asked to do more for less (bonuses are dismal). People who love to give up their time to sleep, stay fit, and spend time with family and friends (all of which are things leadership encourages employees to do to maintain healthy and productive personal and work lives), may struggle to keep up with the demands of the job and may even burn out. Some who struggle, leave the company, resulting in even leaner teams.