Pros
GLG recruits talented individuals from top universities. However, it should be noted that the bulk of these individuals do not have degrees in Finance, Economics, Business, etc. These are the degrees you would expect to see for a company that pitches itself as a Financial Research Firm (which is pretty much the definition of False Advertising). Instead they are in Public Relations, Journalism, History, etc.
Cons
The absolute most boring monotonous work. A Research Professional at GLG (Senior Associate, Research Manager, Senior Research Manager) is truly a glorified call scheduler. You will receive an email or phone call from an Investment firm that has a contract with GLG and be asked to assist them with their research. This is done by searching a database of hundreds of thousands of individuals and finding someone who can speak to the client on the topic they are looking to learn about. You then schedule a time for the two individuals to speak on the phone. After, they speak you then log that you scheduled a phone call and ask the client if it was informative. If you schedule enough phone calls you then get a promotion. Literally that is it, it is terrifyingly boring and you will get zero career development after 2 years. Make no mistake if you stay with GLG for over 4 years and look to transition into another field you will have no clue what you are doing. Stay away the warning signs have all been posted here.