What is the difference? We currently have a 0+ isofix seat. We are looking at the next size up for when DS is bigger, have seen one that is 0+,1,2,3 groups rear facing 0+ and 1 are isofix, then when converted to group 2 and 3 forward facing and isofit. What is isofit and why can't it be isofix at all stages? Am I going to have to faff around with the seatbelt? If so I'll look at something else, we've had a travel system from this brand though and like it. I've googled but I'm none the wiser.