Is it okay to use the headrest’s fixed height positions all the time while using the car seat rear-facing?

Yes, that’s fine, as long as you regularly check that the headrest is in the correct position in relation to your child. However, we do recommend not making a habit of locking the headrest “just because”, since the protection in case of a collision comes from having the harness correctly fastened – not from having the headrest lever set on “Lock”. The headrest brake is mainly used when the child is very small or when traveling with an empty car seat.