I find that fat burners are only really useful to me for the last bits of stubborn fat.
I also find that fat burners with caffeine in them also really drain me of energy and I suspect that the high caffeine elevates cortisol, which in turn will trigger insulin which can equal more tummy fat, which is not really all that desireable.
They are an aid to fat burning, but they don't do a whole lot unless you have your diet and training in order.