Depending on the age of your Kia Niro, the maximum charge rate is either 3.3kW or 3.8kW, although in practice there is little difference in charging times between the two. A 7kW charger will not charge your car significantly faster than a 3kW charger, although depending on the specification of the charger options it may give you additional benefits such as being able to preset charge times to take advantage of cheaper electricity during the night and controlling the charger through a dedicated app. A 7kW charger will not cause your car any harm.