I'm not sure what site said the Be Quiet case felt "frail", it is crazy big and heavy. It is made out of pretty thick steel, so it is extremely sturdy. While building with it, I the term "frail" did not enter my mind once.
Outside of that, I really like it. It's very quiet, and I was able to install 3 x 140mm fans in the front. The only thing I didn't like was installing the power supply. Since the case is so modular, the PSU installation was more complicated than it needed to be. However, since power supplies last for a long time, it's not something a person would have to do more than once or twice.
Here's a thread I did when I switched from a Fractal Design R5 to the Be Quiet case:
https://forums.anandtech.com/threads/be-quiet-dark-base-900-build.2555530/