I've never been a research fellow like this but two friends had differing experiences - I'll tell them in the hope that one might be relevant. In the first case, it was a fixed term 1 year post with the possibility of extension if he brought in funding (no luck in the end). He was expected to publish from his PhD while awaiting the results. He found it quite an isolating experience - there was no mentoring or any sense that anyone was really interested in him. The second case was where a friend joined a research centre on an open-ended contract. Basically she was expected to act as a research assistant on other already-funded projects while applying to be a PI herself. There was quite a lot of flexibility expected of her, but on the other hand so long as there was grant money coming in somewhere, they kept her on even though her initial applications were unsuccessful.