I'll let OP decide on preferred seat. A few thoughts:
I must say I totally prefer my Swedish seats over my US ones for rear facing, they are just so much easier and have a far more solid install. They also sit lower than the radian so you can still see out the back & I have had my radian (with angle adjuster) fall over twice while going around corners, despite having a super tight install, so I have lost all faith in it.
Things are moving forward in US, although very slowly, regarding better seats. After having lived in US for 15 years I think it's a bit sad to see that Sweden had better seats in 1995 than US has today. Hopefully that will change at some point.
On a side note..... Diono is actually trying to have their Radian approved for the European standard but are having lots of issues. What they are trying to do is very interesting and I stay in regular contact with them regarding the project. They want to approve Radian to 25 kg rear facing but without a support leg. And also without tethers. This has never been done before so it's very interesting.
Having a seat approved to 25 kg without tethers would in my opinion be a nice selling points for many parents since installation is far easier. The ECE R44 standard is more strict than the US FVMSS 213 regarding rebound. It's therefore not possible, or at lest extremely difficult, to pass testing to 25 kg (55 lbs) without tether straps.
Diono has also talked about passing the Plus Test to 25 kg. No support leg, no tethers and passing Plus Test to 25 would be fantastic. Without saying too much it was clear from previous conversations that there would be some issues. The seat is now being redesigned for Europe so it will be slimmer, have better lockoffs, etc.
One huge issue with Radian is that it often needs obscene amounts of space. Even with the angle adjuster. A slimmer seat but still with tall seat shell would be welcome. I really hope they can make the seat work and reach their goals. Exciting!!!
If god forbid you do get into an accident with a foreign seat, the fact that the child was improperly restrained is going into the accident and insurance report, along with the fact that you knew you were doing something illegal. If your child is hurt any number of things could happen... insurance won't pay, you get fined or worse.
This is of course nonsense and nothing but a myth. Everyone in a car is insured, even unrestrained children. There is no problem to get seats reimbursed after an accident. We have done so several times for US parents without any issues.
Be aware that there are complications in installing these seats in US cars. For instance the Two way needs to brace and the Axkid needs to tether- both of which can cause problems with advanced airbags in US cars.
Tethering to a front seat has no impact on airbag function. Same goes with leaning on front seat. Yet another popular myth. We have been installing seats this way for the past 50 years and it works very well.
We now have seats that last just as long rear facing here, that don't have mandatory install features that interfere with advanced airbags.
The installation does not interfere with any airbag function although this seem to be a popular myth. The US airbags are not any more advanced than other airbags. They are more powerful due to FVMSS 208 which assumes any US person is not belted and the airbag must protect from the full impact. In Europe and other places we assume that passengers in front seat are wearing a seat belt so the airbag power is lower. It is after all 2015 and laws regarding seat belts have been in in effect for a very long time.
Manufacturers of safety products in US have an unfortunate habit of forbidding everything which is not mandated by law or federal guidelines. This is understandable due to the legal system but unfortunate. There is no upside for a manufacturer to give something away which they don't have to. If bracing isn't required by law then don't allow it. If tethering isn't allowed by law then don't allow it. Allowing these things, which have no impact in airbags, is no upside for manufacturers and therefore often not allowed.
I would look into the Britax Maxfit or any of the Isize seats. Way easier to install and SIP tested.
I'm confused about the "SIP tested". Max-Fix 2 is a nice seat which has the same seat shell as Max-Way and it's very easy to install with Isofix. It will last a year or more longer height wise compared to Dualfix which has a shorter seat shell.
MF2 is not "SIP tested" more than any any other seat. The fact is that any good rear facing seat has excellent SIP. This is due to pre-impact braking and forward momentum. MF2 is approved for the ECE R44 standard which does not require any formal side impact testing. The manufacturers do of course do extensive testing themselves.
MF2 has the same seat shell as Britax Max-Way which is installed with seat belt. MW has passed the ultra strict Swedish Plus test up to 25 kg while MF2 has passed to 18 kg which is maximum for Isofix seats.
I called the Audi dealership and checked with a tech on potential problems with tethering and the airbag sensor. He said the only sensor in our car is located in the middle of the seat, “where your butt goes” and the tethering would not interfere.
Tethering does not interfere or have any impact on airbags.