When we looked into the process, it became clear that French bureaucracy was much greater than almost any other school system & government system our child was looking at.
That would be the biggest con imo. Not only do you need to be a self starter, you also have to be adept at working through red tape and delay.
Also, there is an understanding that not all students will pass courses, graduate on time, etc. It is very much sink or swim environment. There won’t be an existing support system to help if problems arise.