I need to buy an additional ERF seat for my toddler to use in grandparents cars. We have a Britax isofix ERF as the main seat. We got an isofix one as with our infant carrier as our car and grandparents' cars seatbelts were too short to go round the seat. But the ERF seats are so pricey. I'm interested to know if the Joie Stages or any other belt fix ERF seat fits in your car, even if a Cabriofix infant carrier didn't....? Thanks!