We bought a maxirider this time round because with DD1 she was well out of the biggest booster seat on the market by the time she was 4 (eye height). The maxi AHR *is* extendable, just make sure if you are using a regular seat belt that you use the clip that comes with it at the bottom, as it prevents the child from slipping out under the belt (it's called submarining and can cause serious injuires to the chest & throat region). It is worth getting the instruction book out and reading it again to make sure you're still using the seat safely, kwim?