How long should a child stay in a high backed booster?

[Butternutissquashed]

Just that really. Is it weight depdendent, height dependent or down to age? Or a combination of all 3? Is it worth putting him in a booster or should I just use this one until it's not needed?
Thanks

They need to be in a car seat until they are 135cm or 12 years old (whichever comes first) most Hbb go to 36kg so for most will be fine to the age they don’t need one

www.childcarseats.org.uk/types-of-seat/booster-seats/

Sirzy is right about the minimum age/height to stop using one. However it is recommended to use them until 150cm if possible. I think personally it depends on the child's build and the type of car - I would continue to use some form of booster until the child can sit properly on the seat, which means that their knees bend over the edge of the car bench seat while their bum is at the back of the seat. Otherwise, they tend to scoot forwards in order to bend their knees which causes slouching in the belt - the lap belt will come up across their soft abdomen, and the shoulder belt will cut across their neck. This can cause injuries in a crash known as "seatbelt syndrome" which can be serious.

Personally I plan to use the high backed booster until my son physically isn't comfortable in it any more, and then a simple booster until he is 150cm, as we live in another European country where the minimum height is 150cm. But I'm okay with using the simple booster for occasional journeys or tricky situations, from 125cm onwards which is the current recommended minimum height for one. They are so cheap that it's worth getting one for friends or spare, although if you don't feel you'll need one, you can probably get away with the high backed one only.

IME high backed boosters easily last until 135cm but may not fit until 150cm.