From my limited experience its an utter, unmitigated disaster! Twice as many buttons to press to achieve the same outcome as FMGC 1 and countless system bugs leading to major failures. The only improvement over FMGC 1 was the ability to retain 'abeam' points when performing a 'Direct To', yet even that is riddled with bugs which can cause you to bypass the holding fix you planned to go direct to anyway. Rubbish!