We changed to this when our daughter was 6 months old. The Osann can or must be mounted against the direction of travel at this age (makes a small difference in the mounting - for example, you have to tighten a belt over the rear seat), it can also tilt / tilt, so a slightly lying position is possible like a kind of baby car seat.
BUT: Better a portable Maxi Così, we were initially very happy that this could be easily removed and taken / carried. The Osann is a "fixed" installation. I also find the shoulder straps very impractical to adjust. So you would probably be better off with a "mobile" child seat because you don't have to fasten the baby in the car but can do it at home. Greetings