Black box everywhere. Zero knowledge sharing. Old tech stack. I personally didn't grow in terms of skillsets or understanding of the market. The longer I stayed in the company, the more anxious I became about my career. In fact, it was a huge struggle for me to find a new job, partially because the experience with the company was not quite relevant to what the job market wanted and partially because the non-compete was extremely long. I was encouraged to explore as much as I wanted, but no one ever provided any guidance to where to look or how to start. It was a disaster, as I had zero background in the area. It's like teaching someone to swim by throwing him into the sea (not the pool) without even a life jacket. It's true they have a flat structure, but it's not family-like to me at all as advertised. It could be a good place for some people, as there definitely were extremely happy employees. But it's not for me; and I consider my best day in the company the day I resigned.
