just isofix or isofix and top tether?

[FloJo151]

does anyone know why some car seats (without support legs) are able to be fixed to the car with just isofix when they have a top tether too ( like the britax duofix) while others say you need to use the isofix and top tether (like maxi cosi milofix)?

[Blueprintorange]

It depends on the car, the shape of the seats etc. Some seats are a better fit for some cars than others

[AliceMum09]

I'm not sure, but I think it depends on the design of the seat rather than the car it's being fitted in.

Britax must have tested the Duofix both with and without using the top tether.