A characteristic of the FLS is that it can only be used for straight-in approaches. It is not compatible with curved RNP-AR approaches.
For curved approaches, crews need to undertake specific training and checking, and use the FINAL APP (or APP-DES on A350 aircraft) mode.
Airbus is working towards co-existence of the two modes so that all non-ILS/MLS approaches are flown in FLS and the FINAL APP mode remains available for RNP-AR.