Great colleagues, but inefficiency and nepotism
Pros
High salary and good health insurance. Connections to all fields of physics and a vibrant community of young aspiring colleagues. Great potential to learn from others and extend your horizon.
Cons
The skills you acquire do not match the ones needed in industry. With every year spent you loose qualification in the outside world and are forced to a career in science. The tasks for an applied fellow are often regular and repetitive duty work than research. The infrastructure is very bad, offices are small, services factually non-existent. If you have a problem, nobody will help you. If you ask for help, it will be used as an argument against you. As an example, it took me two weeks and several emails and phone calls to get scissors. Rising up in hierarchy does not depend on the quality of your work but on how convenient you were to your supervisors. Scientific arguments or criticism makes you inconvenient to be dealt with and works against your career options. Almost all staff positions are filled with former fellows since, I quote, "we try to give follow-up positions to all of you". Your supervisor is most likely selected due to his ability to work without complaints and not due to his leadership or project management skills. Do not expect guidance or valuable feedback, but be aware that you enter a complex game of social and professional dependence and struggle for visibility.