Full prof is nice for the modelling and much else. I went to the ICDD course in Philadelphia and they recommended it as complimentary to their software. So if the best in the business recommends it, I like it too.
I haven't found a particular need to use it, for much of what full prof offers a lot of the JADE software takes account for what I am asked to find. But I HAVE full prof, and am looking for opportunities to use it.
To use it.. You need some familiarity, it is not straightforward and the GUI is an antique version of DOS. Take your time to familiarize it, and come back here to ask specific questions.
I think GSAS is a good option for modeling. I started on my own, had no help, learnt everything on my own. Now I am very comfortable with it. It took me about 6 months(I was learning it part time only). Appears little difficult initially, but enjoyable later.
Never tried my hands with FULLPROF. Good for beginner and helpless.