Gary/John:

The three in one car seat solution is almost as successful as the 3 in 1 printer/fax/scanner solution (not at all). You really do need a separate infant carrier, baby carrier, then toddler restrainer.

The infant carrier (rear facing) is meant to deal with lateral force by keeping the child prone. Head injuries are further reduced by adding the ubiqutious doughnut around the child's head.

The child carrier should be used rear facing as long as possible for the same reasons. A child's greatest enemy is a heavy head, weak neck, and forward/backward force. By keeping the child as close to prone as possible, you reduce these forces on the child's neck.

When the child is large enough to be forward facing, the iso fix system attempts to keep the car seat top from launching forward. Try this: Kneel in the front seat of your car and grab the top of the car seat that you have "properly" installed without the isofix. Yank forward with all of your might and let your wife measure this distance. Attach the isofix and try again. Even a few inches of play is enough to snap your child's head too fast and cause injury.

Spend the extra $ (you already have, you drive a Volvo) and get the best darn seats you can buy.

Morris