The main negative aspect is that the company has been unable to produce good returns in a long time and as a result is unable to generate enough revenue to pay its employees in line with their market value (even in a second-rate financial hub like Paris). They do not raise base salaries to match inflation.
After a few years, most researchers hit the wall because there are only so many senior positions and they are already in the hands of people who are decades away from retiring. In addition, senior people are sometimes hired to fill in those spots and they remain in place, whether they are exceptionally good or blatantly incompetent. This can be disheartening.
Someone who is thinking of joining CFM as a researcher should also consider how research is conducted: it is very academic. The “science” behind a strategy is as important, if not more, as its profitability. This might not be for everyone.
This is a good place to work if you are young and want to learn because you will be given good mentorship. This is also a great place to work if you want to secure a decent and steady income that lets you focus on other aspects of your life. Since it does not have the downsides of a real hedge fund, it does not have its upsides either: good or bad year, you won’t make real money.