What do you want to know? It's got it's plus and minus points when compared against the RN. Plus, it depends what he wants to do in the RFA. Be ready for lots of sea time, of course, as that's all the RFA do! None of these cushy shore posts!
You cannot sum being at sea to a few words... It's sh1t at times, but it's also the best thing ever at others... and the people are the greatest...
Could he stick with it for ever? It's great fun, I will say that. But it does take it out of your life. I miss the RFA (well, the people I worked with) just about every day, and would say go for it, but not before looking at what the alternatives are...