The restrained system for infant carriers, also known as group 0+, has a different set of requirements as these seats are solely used as rearward facing seat.
Maxi Cosi applies 3-point-harnesses in all its group 0+ car seats because it keeps the baby exactly in the safest position, is easier to tighten and allows to get the baby in and out of the car seat more easily. Both ADAC and Maxi Cosi internal tests show that as infants travel in a rearward facing position the loads of an accident are mainly transferred to the shell of the car seat, and the remainder is spread over the shoulder webbing. The main purpose of the 3-point-harness is to keep the child inside the protective shell of the seat; inside the safest position. Additionally, a 3-point-harness is easier to tighten then a 5-point-harness since there is less friction of the belt in the tongue. As an effect, the chances are higher that the baby is secured tight enough.