Cybex sirona - go for isize or not?

[MyCatLikesToSitInBoxes]

I just wanted to gather some opinions on how much of an improvement to safety isize is. I think we're going to get the cybex sitona for dd - we want to keep her rear facing for as long as possible. But I'm not sure whether to get the isize or not. The big con is that it doesn't swivel which I think makes it a lot less user friendly. If the payoff is that the isize is much safer then I'd go for that, but if not, I'm inclined to go for the original sirona. What have other people done?

I don't think there will be much safety difference at all. The new I-size regulations are a bit stricter with their testing, and include a side impact test which the old R44/04 standard doesn't, but all the big manufacturers have been doing their own in-house side-impact testing to the same level as I-size requires for many years anyway.

You do know that the Sirona has a very short seat shell, it's probably the 'shortest lasting' rear facing seat you can buy. It won't keep an 'average' child rear facing until they are 4.

I've never had a swivel car seat, it's very easy to get a child into a rear facing seat because the car door doesn't get in your way. If you go for something like the Britax Multi Tech II, Two Way Elite or Axkid Minikid those seats have low sides too so that really helps. Those seats go up to 25kgs rear facing, you might want to consider those seats if your child is on the upper centiles of the growth charts.