Just in case anyone is looking at Booster seats for the F56: I bought two models from britax to field-test. I went with the Frontier90 because of the 'click-tite' system, essentially a ratchet that cinches down on the lap belt. Very secure fastening. Otherwise, the differences between this and the Pioneer70 are cosmetic. They were nearly the same size, with the Frontier having a heavier and taller spec limit for the occupant. Kept the Frontier, returned the Pioneer. Anyone having any questions, give me a shout. PS this replaced one of my Britax car seats for the older youngling, the other one still in the car seat and not quite ready for booster. So have a booster and a car seat side by side.