Yeah, I am not a fan. I would only advise you to work for them as long as you find yourself another job. I had my superior not answer my emails even when they wanted me to sign a change in our contract retroactively (I mean how is this even legal?) Nope, I was not worthy of knowing why they wanted me to sign this.
But they did little to find me another project after the first one ended, they tried lowballing me with jobs far below my level of expertise, although they had plenty of fitting jobs for me on their homepage. I got fired which I still think was not really going according to German labour laws. To accept it I asked for a specific kind of Arbeitszeugnis (which is a document from your employer detailing your performance). To me it did not come as a surprise that after the court order in December I had to send them several official reminders just for them to send me a lesser version of what I asked for - in February….
The effects of their incorrect behavior are long lasting and bad for my career.
I really would not recommend anybody to work for them.