AEG Santo larder fridge always frosting up

Our fridge persistently frosts up…needs defrosting every couple of weeks. Its about 2 years old.Called out an AEG approved engineer who showed me how to fully defrost it. There are no symbols on the display to indicate any internal / circuit board problems and the seals look good.He said it is not a true fridge technically because it relies on dynamic air circulation within the cold box ie the fan drawing air over the fins behind the plastic back panel which once they ice over, quickly reduce the fridge effectiveness. We have quite a warm kitchen and the kids often open the door but they always shut it quite quickly. Its an expensive fridge but I don’t want to call an engineer out who just defrosts it and says the type of cooling system it has means it needs frequent defrosting. I’d rather put £65 or whatever he cost towards a new, conventional fridge. Any opinions or similar experiences would be really appreciated.