It is very common that any new electronic part will have to be accepted by the vehicle ECU and that usually means a dealer fit.
Repairing the boys Merc with used parts, the air bags are not accepted so had to fit the ECU from the car the replacement airbags came from.
Many new cars are being scrapped due to ECU faults and that unit can cost a lot of money.
BMW fit them on the rear floor in some cars and if the car enters deep water, it is killed.