As I live in ( sunny ? ) Wales, ill admit to having fitted only one or two water softeners.
In the most recent install I fitted a 300 litre accumulator, post softener, so I can't document or comment on the individual performance of the softener ( as a stand alone item ) I'm afraid.
However.
This does form a good exchange, adding another important consideration for 'ye' of hard water' when designing the DCW system, ( the system which also will end up providing the energy required to propel your DHW out of the outlets ), as losses from such resistances created by such additional / peripheral equipment may easily be overlooked when deciding whether an accumulator is required or not.