matspart3,
Where I fly (N of England), I always ask for FIS when outside my local class D airport environment, as that is what I learned during my PPL training from my instructors. We generally get a good level of traffic information with FIS, workload permitting. I don't ever recall hearing anyone ask for a RIS.
But we have a lot of fast miltary a/c in this area, and I sometimes worry that FIS is not a sufficient service. I have asked several instructors to spell out the difference between FIS and RIS in terms of traffic advice, but I'm not sure I ever got a clear and concise explanation. Could you clarify whether RIS would necessarily give me a better service wrt traffic proximity (both slow and fast), and whether there is any advantage asking for RIS when most if not all a/c in the FIR ask for and get FIS.