Bigger is not always better, it is better to invest in good quality products that will pay back dividends. It is very important to size the water softener correctly. Having a water softener that is too big will cost more money to buy and install due to the extra size. Going too small will produce very unsatisfying results. A small salt based softener will just simply run out of soft water and leave you with hard water again. This erratic water supply produces an erratic performance of washing machines and dishwashers. Over time the amount of cleaning needed will also change for the worse.
So how do I size a water softener?
It is best to base the water usage on 150 litres per day. However, how quickly the water is drawn through the stop depends on the hot water system. If you don’t have a cold water tank, then the water is drawn at the same rate that it is used. Whereas if you do have a cold water tank then you have a buffer system. In other words, you have stored water which is delivered at a slow rate.
So the person without a cold water tank needs a water softener sizing according to the demand by the minute. The water softener sizing will normally be called a High Performance water softener.
What about water conditioners.
Surely with water conditioners, bigger is always better. Yet again, 
the answer is no. It must be sized correctly to produce the desired result. An Aquabion will work much better when there is water surging through than if the water is trickling through.
Under sizing water conditioners
This of course will never produce satisfying results. The treatment will be constant, but not matching the best performance the water conditioner could achieve. Combine this with the performance of many of the water conditioners in the market place varying from 30%-97% (aquabion achieving the higher figure), decreasing this figure by under sizing, is only going to lead to unhappy customers.
Conclusion
If in doubt about water softening sizing then ask!