Booster Car Seat Safety Do We Have To Use A Booster Seat Or Can He Stay In The Car Seat?

Do we have to use a booster seat or can he stay in the car seat? - booster car seat safety

My son is in the maximum weight and height of the seat convertible (40 inches tall and 40 kg), but not quite 4 years old. He is happy in her car seat and personally I prefer it in the car seat safety to stay. However, do not want to compromise by putting it in a car seat that the maximum weight and height has exceeded limits on. Can they still has the additional benefit or protection of your car seat, it is time to use a booster seat?