No, it will not impact your flow rate.
However, it is important to select the correct unit for your application. To choose the correct unit, compare your average/maximum flow rates against SofterWater Conditioners Model Application guide.
The T56, for example, is specified as having a Minimum flow rate of 41 L/min, Average flow rate of 56 L/min and Maximum of 65 L/min.
It’s important that you don’t get a unit that is too small or too large, as it may be less effective due to impaired galvanic activity.