Top tether for britax duo carseat

[DillyDallyDayDream]

I have the britax duo carseat installed in my car using isofix. Just been reading about a top tether. Do I need this? What does it do?

[notfarmingatthemo]

It depends if in the car fitting list if you look up you car it will tell you weather or not you need one for your car. For some car you have to have it for others its a option.