I have gained weight so far on 5:2, but I know its early days. I fast on the days I go into work, as other commitments would make it difficult on 'home' days. I am yet to feel any reduction in appetite, and feel hungry both on fast days and on feast days when I eat plentifully. I'm going to calorie count my feast days, so I have more accurate picture of what I'm consuming. I keep carbs low most of the time.
Advantages of daily calorie control
I was losing weight on it
I can eat with my colleagues at work
Advantages of 5:2
Principle of dieting on days I work, so I can be relaxed at weekend really appeals
Health benefits (although they are long term, so dont have an immediate attraction)
It fits in with my belief we should more naturally, so go for periods without food