Short summary: don't waste your time with the General Service Staff positions.
They posted a job that fitted very well my competences, I applied online via an awful website where they ask you plenty of questions about you and your professional experience. It took me hours to fill all the information there.
I was phoned from one day to another very rudely to ask me if I'd be available a certain day for the interviews, I replied it should be ok and hours later I got a mail saying I'd be interviewing that day: first a test and later a panel interview with the list of people who would be interviewing me. Nothing else about how the interview process would be.
The day of the interview I arrived to the technical test and when I saw the questions, I realized the job was quite different of what I was expecting from the job offer. I did the test without much interest and waited for the panel interview. In the beginning of the panel interview they gave me a better explanation of the role and it confirmed it wasn't for me. I did the interview quickly, left and forgot about it. Never got a positive or negative reply.
I forgot about it until recently I met somebody working at IARC. It turns out the position I interviewed for was already for somebody working in another position and they had to do all this theater where they try to find a good external candidate. Very disappointing.
I also have been told that the general service position have very few promotion opportunities.
