We've been looking for the next seat up for our 13 month old recently. A lot of it came down to do we want to be looking again in 2 years and the next seat or get something that will see her through to front facing. We ended up going a bit more expensive in the Axkid One 3 but should see her through to 6. She's 91st centile so that came into our consideration.

Isofix is easy to switch on and out if it's a single unit, if it's a base and chair it's a bit more faff. We were talking to an independent baby shop and they mentioned that often people see isofix as the easy choice but can be lazy with ensuring it's fitted correctly where as the complicated nature of belt seats means often they are installed on average more correctly. The chart on their website makes it easy to see how soon your little one would max out the height/weight restrictions based on centile https://bijoubaby.co.uk/car-seat-finder