Some other benefits of high back booster seats are the much lower price, far easier installation and also that it's easier to move to another vehicle. (carseat.se)
Some crash tests have shown much better results with high back boosters for keeping the child more stable in a crash. (bestcarseathub.com)
Children sit forward facing in high back boosters (rear facing longer than age 4 would be far safer and preferred). (carseat.se)