HBB with Isofix

[WaftyCrank]

Are these safer than a HBB fitted with just a seatbelt? I'm guessing they are as they are held into the car with the Isofix rather than just the child's weight and seatbelt.

DS is 3.5 and weighs nearly 18kgs. He's currently in a Britax Elite but the top of his head is near the top of his car seat and I think I'm right in thinking I need to take him out of it once his head is over the top? Not his eyeline?

I've been looking at the Britax Kidfix but is there any others I should consider?

TIA

We have the kidfix we are very happy with it are nine year old sat in lots when looking for a second seat for her sister in dh car. kidfix was the most comfortably, it also goes up a long way.

I don't think it is really any safer when the child is in it although it is more stable so doesn't move when they are getting in it, which may make it easier for them to strap themselves in.
It is safer when they are not in it as it is still fixed to the car so wouldn't move in a accident. With non isofix you are supposed to strap them in