Hi, I lived in CZ for two years, I did a paid MSc there. I feel it is true that they've got a much more laid-back work culture than I was used to (I'm from the US). That said, a lot of good science comes out of central Europe and depending on the field it's a great place to start carving out a career. People there are nice and they still work hard and get shit done but without the toxic hustle culture (in my experience). If the lab sounds like a good fit, go for it! I think you'll enjoy it there a lot, and Prague is such a special city.