Pros
I mostly enjoyed the work, the kids are sweet and the books we teach from improved a lot in the time I was there (partially though my help). The people I was working with were mostly nice until the end. The schools you work in can vary, having been there for a few years, I really liked the schools I was in. The work is ideal if you're studying and need a job to pay the bills, but not something you can really do in the long-term. It's precarious work.
Cons
My major problem came in my final year of teaching with Cap'English. When the first lockdown came, I was put on chômage partiel (furlough). This should mean that my employer does not ask me to do anything at all. However, my immediate superior asked me to do some work. I refused, as doing this work would make me an accessory to fraud, and pointed out they shouldn't be asking this of anyone. He then called me and shouted at me. The bosses of the company then emailed me, threatened me with disciplinary meetings for not doing the (illegal) work and included their lawyer. I think I had enough for a tribunal (this was all via email) but I just didn't have the energy to go through with it. Beyond that, the company is fairly typical of one that teaches English in France. The owners of the company do not really know anything about teaching English: they are all graduates of the same école de commerce and have no background in teaching. Before the above event, we got along perfectly well. The pay is not especially good for teaching, I must have been one of their most experienced teachers when I left, I was teaching 18 different groups a week and I did not earn a SMIC annuel and there is no real possibility for advancement. The work is tiring, since the kids are excited to have their English lessons. On an administrative level, the management was a mess. I never got any documents I needed when I needed them, it took at least 2 times of asking and many weeks wait. Their delay in giving me my end of contract papers meant I was without income after leaving for 2 months. When I did get documents they were often wrong. In one notable example, they repeatedly got my gender wrong in my contract (this isn't transphobia or anything, I'm cis and they're just incompetent). This job has taught me something valuable: avoid working in teaching companies that aren't run by people with teaching experience, cause good god what a mess.