@Mave The smart meters record kWh units exactly the same as the previous meters. However some people get bigger bills because a history of estimates is suddenly corrected. You should look closely at your bills and see if you have had estimated readings. Also check the closing and opening readings carefully and write them down when the installer comes.
Insist the installer makes your Display unit work, and also shows you how to take manual readings from the new meters in case there is a problem making them work correctly.
My smart meter was installed just over a year ago. Do I assume it is only a SMET1 and therefore likely not to work with other suppliers. Would like to add that readings have been accurate and not a problem .