Anything that absorbs energy in a crash should be a benefit and improve safety. If it also adds a buffer or space between the child and potential impact against a door, pillar or other intrusion, that's a double bonus. Britax claims a
45% reduction in crash forces for the child in the seat, in addition to a benefit for the adjacent passenger. Plus, it should tend to be a benefit in more situations than internal features like wings and energy absorbing materials like foam and cushions, because the head can easily move forward of those features in a side impact crash with any forward motion involved.
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I have no doubt based on the physics involved in a crash that this is a safety advantage in a side impact, for both front and rear facing. The question is whether or not it has a significant real life benefit or whether it is worth the added cost, and no one can answer that right now. Much the same can be said of almost any other side impact technology and really almost any high end child seat feature. The new Advocate has a lot of advantages and disadvantages compared to other seats. In terms of safety, though, by far the most important thing is to correctly install and use whatever you buy in the back seat of your vehicle. The benefits of one seat compared to another are likely to be very small if you've attended to making sure you are using it right on every trip!