A.V.
I moved DD to a highback booster with harness (Frontier) when she outgrew her Marathon. I expect this to be her last car seat. I've been pleased with the Britax brand and I am IN LOVE WITH clicktight. Easiest friggin installation I've ever had. DD can even install her own seat, if we let her. She is 7 and for now the harness works for us. We have a Bubblebum seat she used on vacation (taxis, rental car) when she was 4.5/5 but she doesn't like not having a back.