My ropey flying had nothing to do with it (this time, at least!
). However, speed control by Autothrust was poorer than expected under conditions prevailing (slightly thermal/gusty, but nothing exceptional) and I attribute it partially to F3 (slower engine response at lower thrust setting).
The bottom line is - we went around, burning 50x more fuel than we expected to save...
I am not saying that F3 should never be used (in fact, my operator has just mandated them as standard/preferred setting). I am just not sure whether actual fuel savings will look as good as they do on paper...