[speedupmate]

just take the science out of it, carseat for a kid does nothing more than to rise them to suitable seatbelt height or makes the seatbelt usable for really young kids.

Isofix does not have to have a leg etc could be just bars holding the seat at place, thats its only benefit it keeps the object attached to isofix in place in case of a accident. It will not fly around the car as it is attached to it thus provides more safety.

At the end if the crash is huge then newtons laws apply a bigger mass will just run everything over, does not matter if it is secured or not you just can't beat a bigger mass.